Extensible Markup Language (XML) 1.0

W3C Recommendation 10-February-1998

This version:
Latest version:
Previous version:
Tim Bray (Textuality and Netscape) <tbray@textuality.com>
Jean Paoli (Microsoft) <jeanpa@microsoft.com>
C. M. Sperberg-McQueen (University of Illinois at Chicago) <cmsmcq@uic.edu>
Lothar Seidel, Frankfurt am Main, September 2017


The Extensible Markup Language (XML) is a subset of SGML that is completely described in this document. Its goal is to enable generic SGML to be served, received, and processed on the Web in the way that is now possible with HTML. XML has been designed for ease of implementation and for interoperability with both SGML and HTML.

Die Absicht, ein vereinfachtes SGML für das WEB zu erstellen, hat sich mit XML nicht verwirklichen lassen. Aber es ist bislang noch nicht die Konsequenz daraus gezogen worden, ein besseres SGML für das WEB zu erstellen, SGML2 oder XML2. Ein erster Schritt dazu soll die nachfolgende kommentierte Dokumentation von XML 1.0 sein. Ihre Hauptaufgabe ist es, die zu einander gehörigen syntax produktions von SGML und XML nebeneinanderzustellen, damit sich jeder selbst ein Urteil bilden kann, ob ein SGML2 oder ein XML2 erstellt werden muss.

Das vorliegende Dokument ist mit der HT app und der DtdEdd erstell.

Status of this document

This document has been reviewed by W3C Members and other interested parties and has been endorsed by the Director as a W3C Recommendation. It is a stable document and may be used as reference material or cited as a normative reference from another document. W3C’s role in making the Recommendation is to draw attention to the specification and to promote its widespread deployment. This enhances the functionality and interoperability of the Web.

This document specifies a syntax created by subsetting an existing, widely used international text processing standard (Standard Generalized Markup Language, ISO 8879:1986(E) as amended and corrected) for use on the World Wide Web. It is a product of the W3C XML Activity, details of which can be found at http://www.w3.org/XML. A list of current W3C Recommendations and other technical documents can be found at http://www.w3.org/TR.

This specification uses the term URI, which is defined by [Berners-Lee et al.], a work in progress expected to update [IETF RFC1738] and [IETF RFC1808].

The list of known errors in this specification is available at http://www.w3.org/XML/xml-19980210-errata.

Please report errors in this document to xml-editor@w3.org.

Extensible Markup Language (XML) 1.0

Table of Contents

1. Introduction

    1.1 Origin and Goals

    1.2 Terminology

2. Documents
    2.1 Well-Formed XML Documents
    2.2 Characters
    2.3 Common Syntactic Constructs
    2.4 Character Data and Markup
    2.6 Processing Instructions
    2.7 CDATA Sections
    2.8 Prolog and Document Type Declaration
    2.9 Standalone Document Declaration
    2.10 White Space Handling
    2.11 End-of-Line Handling
    2.12 Language Identification
3. Logical Structures
    3.1 Start-Tags, End-Tags, and Empty-Element Tags
    3.2 Element Type Declarations
        3.2.1 Element Content
        3.2.2 Mixed Content
    3.3 Attribute-List Declarations
        3.3.1 Attribute Types
        3.3.2 Attribute Defaults
        3.3.3 Attribute-Value Normalization
    3.4 Conditional Sections
4. Physical Structures
    4.1 Character and Entity References
    4.2 Entity Declarations
        4.2.1 Internal Entities
        4.2.2 External Entities
    4.3 Parsed Entities
        4.3.1 The Text Declaration
        4.3.2 Well-Formed Parsed Entities
        4.3.3 Character Encoding in Entities
    4.4 XML Processor Treatment of Entities and References
        4.4.1 Not Recognized
        4.4.2 Included
        4.4.3 Included If Validating
        4.4.4 Forbidden
        4.4.5 Included in Literal
        4.4.6 Notify
        4.4.7 Bypassed
        4.4.8 Included as PE
    4.5 Construction of Internal Entity Replacement Text
    4.6 Predefined Entities
    4.7 Notation Declarations
    4.8 Document Entity
5. Conformance
    5.1 Validating and Non-Validating Processors
    5.2 Using XML Processors
6. Notation


A. References
    A.1 Normative References
    A.2 Other References
B. Character Classes
C. XML and SGML (Non-Normative)
D. Expansion of Entity and Character References (Non-Normative)
E. Deterministic Content Models (Non-Normative)
F. Autodetection of Character Encodings (Non-Normative)
G. W3C XML Working Group (Non-Normative)

1. Introduction

Extensible Markup Language, abbreviated XML, describes a class of data objects called XML documents and partially describes the behavior of computer programs which process them. XML is an application profile or restricted form of SGML, the Standard Generalized Markup Language [ISO 8879]. By construction, XML documents are conforming SGML documents.

XML documents are made up of storage units called entities, which contain either parsed or unparsed data. Parsed data is made up of characters, some of which form character data, and some of which form markup. Markup encodes a description of the document’s storage layout and logical structure. XML provides a mechanism to impose constraints on the storage layout and logical structure.

Die logical structure in SGML und XML ist die deduktive Struktur der Elemente als ein teilehabendes Ganzes.

A software module called an XML processor is used to read XML documents and provide access to their content and structure. It is assumed that an XML processor is doing its work on behalf of another module, called the application. This specification describes the required behavior of an XML processor in terms of how it must read XML data and the information it must provide to the application.

1.1 Origin and Goals

XML was developed by an XML Working Group (originally known as the SGML Editorial Review Board) formed under the auspices of the World Wide Web Consortium (W3C) in 1996. It was chaired by Jon Bosak of Sun Microsystems with the active participation of an XML Special Interest Group (previously known as the SGML Working Group) also organized by the W3C. The membership of the XML Working Group is given in an appendix. Dan Connolly served as the WG’s contact with the W3C.

The design goals for XML are:

  1. XML shall be straightforwardly usable over the Internet.
  2. XML shall support a wide variety of applications.
  3. XML shall be compatible with SGML.
  4. It shall be easy to write programs which process XML documents.
  5. The number of optional features in XML is to be kept to the absolute minimum, ideally zero.
  6. XML documents should be human-legible and reasonably clear.
  7. The XML design should be prepared quickly.
  8. The design of XML shall be formal and concise.
  9. XML documents shall be easy to create.
  10. Terseness in XML markup is of minimal importance.

This specification, together with associated standards (Unicode and ISO/IEC 10646 for characters, Internet RFC 1766 for language identification tags, ISO 639 for language name codes, and ISO 3166 for country name codes), provides all the information necessary to understand XML Version 1.0 and construct computer programs to process it.

This version of the XML specification may be distributed freely, as long as all text and legal notices remain intact.

1.2 Terminology

The terminology used to describe XML documents is defined in the body of this specification. The terms defined in the following list are used in building those definitions and in describing the actions of an XML processor:

Conforming documents and XML processors are permitted to but need not behave as described.
Conforming documents and XML processors are required to behave as described; otherwise they are in error.
A violation of the rules of this specification; results are undefined. Conforming software may detect and report an error and may recover from it.
fatal error
An error which a conforming XML processor must detect and report to the application. After encountering a fatal error, the processor may continue processing the data to search for further errors and may report such errors to the application. In order to support correction of errors, the processor may make unprocessed data from the document (with intermingled character data and markup) available to the application. Once a fatal error is detected, however, the processor must not continue normal processing (i.e., it must not continue to pass character data and information about the document’s logical structure to the application in the normal way).
at user option
Conforming software may or must (depending on the modal verb in the sentence) behave as described; if it does, it must provide users a means to enable or disable the behavior described.
validity constraint
A rule which applies to all valid XML documents. Violations of validity constraints are errors; they must, at user option, be reported by validating XML processors.
well-formedness constraint
A rule which applies to all well-formed XML documents. Violations of well-formedness constraints are fatal errors.
(Of strings or names:) Two strings or names being compared must be identical. Characters with multiple possible representations in ISO/IEC 10646 (e.g. characters with both precomposed and base+diacritic forms) match only if they have the same representation in both strings. At user option, processors may normalize such characters to some canonical form. No case folding is performed. (Of strings and rules in the grammar:) A string matches a grammatical production if it belongs to the language generated by that production. (Of content and content models:) An element matches its declaration when it conforms in the fashion described in the constraint "Element Valid".
for compatibility
A feature of XML included solely to ensure that XML remains compatible with SGML.
for interoperability
A non-binding recommendation included to increase the chances that XML documents can be processed by the existing installed base of SGML processors which predate the WebSGML Adaptations Annex to ISO 8879.

2. Documents

A data object is an XML document if it is well-formed, as defined in this specification. A well-formed XML document may in addition be valid if it meets certain further constraints.

Each XML document has both a logical and a physical structure. Physically, the document is composed of units called entities. An entity may refer to other entities to cause their inclusion in the document. A document begins in a "root" or document entity. Logically, the document is composed of declarations, elements, comments, character references, and processing instructions, all of which are indicated in the document by explicit markup. The logical and physical structures must nest properly, as described in "4.3.2 Well-Formed Parsed Entities".

Der Unterschied zwischen dem Nesting aus der entity structure und dem teilehabenden Ganzen aus der element structure wird bei der Gegenüberstellung von Programmschleifen und einem document element deutlich:

if 1 then 2

if 2 then 3

if 1 then 3




Wenn 1, so 2, wenn 2, so 3. Aber nicht umgekehrt, wenn 2, so 1 oder wenn 3, so 2. Denn viele der 2 sind nicht 1, und viele der 3 sind nicht 2.

Aus den beiden ersten ifs ergibt sich mit Notwendigkeit das dritte if, wenn 1, so 3, aber nicht umgekehrt, wenn 3, so 1, weil viele der 3 nicht 1 sind.

Fußnote: Ob die zeichnerische Darstellung mehr als nur eine Veranschaulichung der Implikation ist, denn das if ist nicht Teil des then, und ein Teil des then ist nicht das if, bleibt zunächst offen.

Das Ineinander der Elemente einer Dokumenteninstanz A von SGML oder XML sieht so aus:

<a> A = B

<b> B = C

<c> A = C




Ein Teil des Element A ist das ganze Element B.

Ein Teil des Element B ist das ganze Element C.

Ein Teil des Element A ist das ganze Element C.

Element C enthält Element B, aber nur einen Teil.

Element B enthält Element A, aber nur einen Teil.

Element A enthält alle Elemente ganz und ist selbst in keinem weiteren Element enthalten.

Um diese beiden Schlussfolgerungen und diese beiden Zeichnungen dreht sich nicht nur die lange Geschichte der Logik, sondern auch die kurze Geschichte der markup languages. Denn es handelt sich bei diesen beiden Gedankenfolgen um die Vertreter zweier logischer Wissenschaften, die ich als die 123 Logik und die ABC Logik bezeichne, die Logik des Getrennten oder die Mathematik und die Logik des Geteilten oder die Ontologie.

SGML descriptive tags are the antithesis of procedural language commands, and document type designers, in particular, should be discouraged from thinking them as similar. SGML Handbook, Annex F.1, A Model of SGML Parsing, S. 544

Mehr über die lange Geschichte der Logik in wahrheit. Mehr über die kurze Geschichte der markup languages im alten Weg und im neuen Weg von SGML.

Dass ich als ABC Denker zu wenig vom 123 Denken verstehe, ist keine Ausnahme, sondern die Regel, genau wie umgekehrt die 123 Denker oft wenig vom ABC verstehen. Dass ich dennoch mit dem Anspruch auftrete, den 123 Denkern das ABC nahezubringen, hat seine Ursache in meiner festen Überzeugung, dass die mathematische Logik erst dann ihren Höhepunkt erreichen wird, wenn sie mit den wenigen Regeln des Geteilten vertraut sein wird. Denn die mathematischen Dinge sind in allen Dingen der Welt oder des Seins. Da wäre es gut, wenn die Mathematik die ontologischen Grundlagen der Logik kennt.

2.1 Well-Formed XML Documents

A textual object is a well-formed XML document if:

  1. Taken as a whole, it matches the production labeled document.
  2. It meets all the well-formedness constraints given in this specification.
  3. Each of the parsed entities which is referenced directly or indirectly within the document is well-formed.

Für die Entscheidung, XML2 oder SGML2 zu entwickeln, müssen die vergleichbaren Daten beieinander sein. Die XML productions sind daher mit den ihnen entsprechenden SGML productions verknüpft, und zwar in ihren production numbers [nn] rechts neben <!PRD. Gibt es in SGML keine Entsprechung einer XML production, gibt es keine Verknüpfung.


[1] documentprolog element Misc*

Um XML einfach zu halten, haben die Autoren die mehrstufigen Definitionen von SGML oft einstufig gemacht.

In SGML ist die document entity [2] nur eine, die wichtigste entity des SGML document [1]. Aus der document entity werden die anderen SGML entities in beliebiger Anzahl und Folge aufgerufen. In der document entity befindet sich unter anderem das document instance set [10], das in XML das document ist. Damit ist das XML document ein Monolith, in dem es in XML keine entity stucture gibt.

Die Syntax in den productions ähnelt der im content model mit einer Ausnahme. Das seq in den XML productions ist ein Leerzeichen, siehe 6. Notation. Die beiden Leerzeichen zwischen prolog element Misc* bedeuten, dass die drei nach einander in der vorgegebenen Reihenfolge auftreten müssen, wobei Misc null- oder mehrfach auftreten kann.

Das eine element zwischen prolog und Misc ist das document element. In ihm befinden sich alle anderen Elemente.

Matching the document production implies that:

  1. It contains one or more elements.
  2. There is exactly one element, called the root, or document element, no part of which appears in the content of any other element. For all other elements, if the start-tag is in the content of another element, the end-tag is in the content of the same element. More simply stated, the elements, delimited by start- and end-tags, nest properly within each other.

Die Elemente sind kein Nesting, sondern ein teilehabendes Ganzes. Jedes Element ist Teil des document element und somit mit einem Teil des document element identisch: Der Absatz ist ein wirklicher Teil des Kapitels, das Kapitel ist ein wirklicher Teil des Buchs, während das document element in keinem weiteren Element ist. Aus dem Teilsein ergibt sich, dass die Teile entweder vollständig ineinander sind wie das Kapitel im Buch oder dass sie vollständig voneinander getrennt wie die einzelnen Kapitel in einem übergeordneten Ganzen sind. Sich überlagende Teilmengen können zwei Elemente in einer XML Deklaration oder einer SGML Deklaration nicht haben.

As a consequence of this, for each non-root element C in the document, there is one other element P in the document such that C is in the content of P, but is not in the content of any other element that is in the content of P. P is referred to as the parent of C, and C as a child of P.

Neben den genealogischen Namen parent und child sind die Relationen des Ganzen zum Teil und des Teils zum Ganzen vorzuziehen, wo es angebracht ist. Bei der eingeschlechtlichen Fortpflanzung aus dem Alten Testament, in der der Abraham den Isaak zeugt oder in der Metaphysik des Aristoteles, wo der Mensch den Menschen zeugt, bedeutet Teil dasselbe wie child und Ganzes dasselbe wie parent. Das ist genauso irreführend wie die Bezeichnung "Hierarchie" für ein teilehabendes Ganzes. Beide Ausdrucksweisen haben Vor- und Nachteile. Die genealogische oder hierarchische Ausdrucksweise deutet eine geordnete Folge an, was der Teil und das Ganze nicht können. Das Ganze kann dagegen als ein Eines der Ursprung sein, und die Teile sind mit den Teilen des Ganzen identisch, die sie sind, was bei Eltern und Kindern, Offizieren und Soldaten nicht der Fall ist. Die genealogische/hierarchische Ausdrucksweise ist für das Getrennte, die des Ganzen für das Geteilte vorzuziehen. Manchmal sind beide angebracht, etwa, wenn die Kapitel numeriert werden.

2.2 Characters

A parsed entity contains text, a sequence of characters, which may represent markup or character data. A character is an atomic unit of text as specified by ISO/IEC 10646 [ISO/IEC 10646]. Legal characters are tab, carriage return, line feed, and the legal graphic characters of Unicode and ISO/IEC 10646. The use of "compatibility characters", as defined in section 6.8 of [Unicode], is discouraged.

Character Range

[2]char #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF] any Unicode character, excluding the surrogate blocks, FFFE, and FFFF.

The mechanism for encoding character code points into bit patterns may vary from entity to entity. All XML processors must accept the UTF-8 and UTF-16 encodings of 10646; the mechanisms for signaling which of the two is in use, or for bringing other encodings into play, are discussed later, in "4.3.3 Character Encoding in Entities".

Eine character range wird der SGML application in der SGML document entity in der SGML declaration im document character set mitgeteilt.

Der SGML character unterscheidet nur zwischen markup character und data character.

2.3 Common Syntactic Constructs

This section defines some symbols used widely in the grammar.

S (white space) consists of one or more space (#x20) characters, carriage returns, line feeds, or tabs.

White Space

[3]s (#x20 | #x9 | #xD | #xA)+

Characters are classified for convenience as letters, digits, or other characters. Letters consist of an alphabetic or syllabic base character possibly followed by one or more combining characters, or of an ideographic character. Full definitions of the specific characters in each class are given in "B. Character Classes".

A Name is a token beginning with a letter or one of a few punctuation characters, and continuing with letters, digits, hyphens, underscores, colons, or full stops, together known as name characters. Names beginning with the string "xml", or any string which would match ((’X’|’x’) (’M’|’m’) (’L’|’l’)), are reserved for standardization in this or future versions of this specification.

Note: The colon character within XML names is reserved for experimentation with name spaces. Its meaning is expected to be standardized at some future point, at which point those documents using the colon for experimental purposes may need to be updated. (There is no guarantee that any name-space mechanism adopted for XML will in fact use the colon as a name-space delimiter.) In practice, this means that authors should not use the colon in XML names except as part of name-space experiments, but that XML processors should accept the colon as a name character.

In SGML sind das colon und der Unterstreichstrich als name character nicht erlaubt. In SGML2 sind die extended naming rules von SGML nicht erlaubt, damit sich Chinesen, Inder und Deutsche in SGML2 mit denselben Namen miteinander verständigen können.

An Nmtoken (name token) is any mixture of name characters.

Names and Tokens

[4]NameChar LetterDigit | ’.’ | ’-’ | ’_’ | ’:’ | CombiningCharExtender [5]Name (Letter | ’_’ | ’:’) (NameChar)*

Der Klammer (Letter | ’_’ | ’:’) entspricht in SGML ungefähr der name start character. Er hat is XML keine eigene production, sondern zählt zu den character classes.

[6] NamesName (S Name)* [7]Nmtoken (NameChar)+ [8] NmtokensNmtoken (S Nmtoken)*

Literal data is any quoted string not containing the quotation mark used as a delimiter for that string. Literals are used for specifying the content of internal entities (EntityValue), the values of attributes (AttValue), and external identifiers (SystemLiteral). Note that a SystemLiteral can be parsed without scanning for markup.


[9]EntityValue ’"’ ([^%&"] | PEReferenceReference)* ’"’ |  "’" ([^%&’] | PEReferenceReference)* "’" Den EntityValue kann man als die [67] replaceable parameter data des parameter literal des entity text ansehen. Durch den literal werden die Gänsefüßchen, durch die parameter data die regex überflüssig. [10]AttValue ’"’ ([^<&"] | Reference)* ’"’ |  "’" ([^<&’] | Reference)* "’" [11] SystemLiteral (’"’ [^"]* ’"’) | ("’" [^’]* "’") [12] PubidLiteral ’"’ PubidChar* ’"’ | "’" (PubidChar - "’")* "’" [13]PubidChar #x20 | #xD | #xA | [a-zA-Z0-9] | [-’()+,./:=?;!*#@$_%]

Die verschiedenen literals werden in SGML so definiert, dass regular expressions wie [^%&"] oder [^<&"] nicht erforderlich sind ([^%&"] bedeutet: keines der Zeichen %, & oder ", wobei ^ nicht bedeutet). Statt der literalen Anführungszeichen ’"’ und "’" benutzt SGML nur die beiden delimiter lit für " und lita für ’.

2.4 Character Data and Markup

Text consists of intermingled character data and markup. Markup takes the form of start-tags, end-tags, empty-element tags, entity references, character references, comments, CDATA section delimiters, document type declarations, and processing instructions.

All text that is not markup constitutes the character data of the document.

The ampersand character (&) and the left angle bracket (<) may appear in their literal form only when used as markup delimiters, or within a comment, a processing instruction, or a CDATA section. They are also legal within the literal entity value of an internal entity declaration; see "4.3.2 Well-Formed Parsed Entities". If they are needed elsewhere, they must be escaped using either numeric character references or the strings "&amp;" and "&lt;" respectively. The right angle bracket (>) may be represented using the string "&gt;", and must, for compatibility, be escaped using "&gt;" or a character reference when it appears in the string "]]>" in content, when that string is not marking the end of a CDATA section.

In the content of elements, character data is any string of characters which does not contain the start-delimiter of any markup. In a CDATA section, character data is any string of characters not including the CDATA-section-close delimiter, "]]>".

To allow attribute values to contain both single and double quotes, the apostrophe or single-quote character (’) may be represented as "&apos;" ("&rsquo;"), and the double-quote character (") as "&quot;".

Sowohl der SGML Editor FrameMaker7.2 als auch HTML4.01 haben vergessen, apos (=lita delimiter) in ihre entity Sammlungen bzw, ihre Lese- und Schreibregeln aufzunehmen. Das hat zur Folge, dass &apos; in der letzten vorhandenen SGML Software nicht round-trip-tauglich ist, nur in den SGML Editor importiert, nicht nach html401 exportiert werden kann. Es kann daher in der vorliegenden Dokumentation nicht verwendet werden. Dagegen ist rsquo sowohl im W3C HTML4.01: <!ENTITY rsquo CDATA "&#8217;" -- right single quotation mark--, auch in FrameMaker7.2 verwendbar. Das ist zwar typographisch nicht ganz in Ordnung, erfüllt aber seinen Zweck. Die hexadezimale Nummer 8217 interessiert den SGML Parser nicht, weil er derzeit nur dezimal bis 256 zählen kann (Daher kann der entity text leer "" sein.), nur der Name rsquo und die Herkunft aus einem der ISO entity sets interessieren ihn. In der html401 Dokumentation von XML wird daher anstelle von apos rsquo verwendet.


Character Data

[14]CharData [^<&]* - ([^<&]* ’]]>’ [^<&]*)


Comments may appear anywhere in a document outside other markup; in addition, they may appear within the document type declaration at places allowed by the grammar. They are not part of the document’s character data; an XML processor may, but need not, make it possible for an application to retrieve the text of comments. For compatibility, the string "--" (double-hyphen) must not occur within comments.


[15]Comment ’<!--’ ((Char - ’-’) | (’-’ (Char - ’-’)))* ’-->’ Kommentare gibt es in XML nur als Kommentardeklarationen außerhalb von Deklarationen. In den Deklarationen, zu deren Kommentierung sie gemacht worden sind, sind sie nicht erlaubt. Da die vorliegende Dokumentation mit einer SGML DTD erstellt ist, können die Kommentare sowohl in den Deklarationen sein, als auch als eigene Kommentardeklarationen erscheinen. Hier sind auch die inclusions aus dem body von html erlaubt, etwa das a element.

An example of a comment:

<!-- declarations for <head> & <body> -->

2.6 Processing Instructions

Processing instructions (PIs) allow documents to contain instructions for applications.

Processing Instructions

[16] PI’<?’ PITarget (S (Char* - (Char* ’?>’ Char*)))? ’?>’ [17] PITargetName - ((’X’ | ’x’) (’M’ | ’m’) (’L’ | ’l’))

PIs are not part of the document’s character data, but must be passed through to the application. The PI begins with a target (PITarget) used to identify the application to which the instruction is directed. The target names "XML", "xml", and so on are reserved for standardization in this or future versions of this specification. The XML Notation mechanism may be used for formal declaration of PI targets.

2.7 CDATA Sections

CDATA sections may occur anywhere character data may occur; they are used to escape blocks of text containing characters which would otherwise be recognized as markup. CDATA sections begin with the string "<![CDATA[" and end with the string "]]>":

CDATA Sections

[18] CDSectCDStart CData CDEnd [19]CDStart ’<![CDATA[’ In der XML production 19 sind die SGML productions 94, 97 und 100 zudammengefasst, weil das status keyword immer CDATA ist. Für die status keywords INCLUDE und IGNORE werden XML eigene Sections deklariert. Vgl. 3.4 Conditional Section [20]CData (Char* - (Char* ’]]>’ Char*)) [21]CDEnd ’]]>’

Within a CDATA section, only the CDEnd string is recognized as markup, so that left angle brackets and ampersands may occur in their literal form; they need not (and cannot) be escaped using "&lt;" and "&amp;". CDATA sections cannot nest.

An example of a CDATA section, in which "<greeting>" and "</greeting>" are recognized as character data, not markup:

<greeting>Hello, world!</greeting>

Die CDATA section ist nur eine Form der marked section mit dem keyword CDATA. Die spätere Definition der conditional section ist redundant, weil sie nur zwei weitere keywords hinzufügt. Das einstufige Definitionsverfahren hat zwar den Vorteil des Einfachen aber auch dessen Nachteil, nur Eines zu können. Die Definition einer Klasse Gleichartiger muss nur einmal gemacht werden.

2.8 Prolog and Document Type Declaration

XML documents may, and should, begin with an XML declaration which specifies the version of XML being used. For example, the following is a complete XML document, well-formed but not valid:

<?xml version="1.0"?>

<greeting>Hello, world!</greeting>

and so is this:

<greeting>Hello, world!</greeting>

The version number "1.0" should be used to indicate conformance to this version of this specification; it is an error for a document to use the value "1.0" if it does not conform to this version of this specification. It is the intent of the XML working group to give later versions of this specification numbers other than "1.0", but this intent does not indicate a commitment to produce any future versions of XML, nor if any are produced, to use any particular numbering scheme. Since future versions are not ruled out, this construct is provided as a means to allow the possibility of automatic version recognition, should it become necessary. Processors may signal an error if they receive documents labeled with versions they do not support.

The function of the markup in an XML document is to describe its storage and logical structure and to associate attribute-value pairs with its logical structures. XML provides a mechanism, the document type declaration, to define constraints on the logical structure and to support the use of predefined storage units. An XML document is valid if it has an associated document type declaration and if the document complies with the constraints expressed in it.

The document type declaration must appear before the first element in the document.


[22]prolog XMLDecl? Misc* (doctypedecl Misc*)? [23]XMLDecl ’<?xml’ VersionInfo EncodingDecl? SDDecl? S? ’?>’ Die processing instruction XMLDecl besteht aus dem minimum literal, der ersten Zeile der SGML declaration, die auch dort die Version anzeigt. Eine EncodingDecl und SDDecl gibt es in SGML nicht. [24]VersionInfo S ’version’ Eq (’ VersionNum ’ | " VersionNum ") [25]Eq S? ’=’ S? Ein schon von alters her vernachlässigter connector/separator. Das = Zeichen wird in SGML nur an einer Stelle, in XML an mehreren Stellen gebraucht. Bingham hat ihm einen Ehrenplatz in seiner Darstellung der abstract syntax von SGML zugewiesen, indem er linke und rechte Seite der Definitionsgleichung durch das = verbindet. Ich habe das in DtdEdd mit dem leeren is element ausgedrückt. Zwar ist es in Wahrheit nur ein separator, damit die beiden Seiten einer Gleichung nicht ohne Abstand zueinander sind, hat aber unabhängig davon die seit alters her vernachlässigte Bedeutung. Mozilla interpretiert im Inspektor das leere is element als Behälter der rechten Seite. [26]VersionNum ([a-zA-Z0-9_.:] | ’-’)+ 24 und 26 entsprechen dem literalen Anfang der SGML production 171: <!SGML "ISO 8879-1989" . [27]Misc CommentPIS

The XML document type declaration contains or points to markup declarations that provide a grammar for a class of documents. This grammar is known as a document type definition, or DTD. The document type declaration can point to an external subset (a special kind of external entity) containing markup declarations, or can contain the markup declarations directly in an internal subset, or can do both. The DTD for a document consists of both subsets taken together.

A markup declaration is an element type declaration, an attribute-list declaration, an entity declaration, or a notation declaration. These declarations may be contained in whole or in part within parameter entities, as described in the well-formedness and validity constraints below. For fuller information, see "4. Physical Structures".

Die parameter entities sind ein Gebilde zwischen dem Getrennten und dem Geteilten. Einerseits können parameter entities innerhalb von parameter entities sein und sind somit Geteiltes. Andererseits sind sie Mengen, die zu Einheiten zusammengefasst werden, also Getrenntes. Tasächlich verläuft die Erstellung einer parameter entity stets nach der 123 Methode vom Kleinsten zum Größten. Als erstes werden die entities für Phrasen erstellt, danach die für Absätze und zum Schluss die für sections and paras.

Document Type Definition

[28] doctypedecl ’<!DOCTYPE’ S Name (S ExternalID)? S? (’[’ (markupdeclPEReferenceS)* ’]’ S?)? ’>’ [ VC: Root Element Type ] [29]markupdecl elementdeclAttlistDeclEntityDeclNotationDeclPIComment [ VC: Proper Declaration/PE Nesting ] [ WFC: PEs in Internal Subset ]

The markup declarations may be made up in whole or in part of the replacement text of parameter entities. The productions later in this specification for individual nonterminals (elementdecl, AttlistDecl, and so on) describe the declarations after all the parameter entities have been included.

Validity Constraint: Root Element Type
The Name in the document type declaration must match the element type of the root element.

Validity Constraint: Proper Declaration/PE Nesting
Parameter-entity replacement text must be properly nested with markup declarations. That is to say, if either the first character or the last character of a markup declaration (markupdecl above) is contained in the replacement text for a parameter-entity reference, both must be contained in the same replacement text.

Beim Ineinander mehrerer parameter entities handelt es sich tatsächlich um ein nesting, weil sie vom Teil zum Ganzen definiert werden müssen. Umgekehrt bei den Elementen, die das nicht können, sondern immer ein teilehabendes Ganzes sind. Zwar gibt es bei den Elementen keinen zwingenden Grund, aber das Einsichtigste ist, sie vom document element über die sections, die paras bis hin zu den phrases zu entwickeln.

Well-Formedness Constraint: PEs in Internal Subset
In the internal DTD subset, parameter-entity references can occur only where markup declarations can occur, not within markup declarations. (This does not apply to references that occur in external parameter entities or to the external subset.)

Like the internal subset, the external subset and any external parameter entities referred to in the DTD must consist of a series of complete markup declarations of the types allowed by the non-terminal symbol markupdecl, interspersed with white space or parameter-entity references. However, portions of the contents of the external subset or of external parameter entities may conditionally be ignored by using the conditional section construct; this is not allowed in the internal subset.

External Subset

[30]extSubset TextDecl? extSubsetDecl [31]extSubsetDecl ( markupdeclconditionalSectPEReferenceS )*

Das externe subset der DTD wird in SGML nur indirekt über den external identifier angesprochen, wie bei dem system identifier "hello.dtd" im nachstenenden Beispiel.

The external subset and external parameter entities also differ from the internal subset in that in them, parameter-entity references are permitted within markup declarations, not only between markup declarations.

An example of an XML document with a document type declaration:

<?xml version="1.0"?>

<!DOCTYPE greeting SYSTEM "hello.dtd">

<greeting>Hello, world!</greeting>

The system identifier "hello.dtd" gives the URI of a DTD for the document.

The declarations can also be given locally, as in this example:

<?xml version="1.0" encoding="UTF-8" ?>

<!DOCTYPE greeting [

<!ELEMENT greeting (#PCDATA)>


<greeting>Hello, world!</greeting>

#PCDATA bedeutet parsed character data, das heißt entweder, markup character und data character gemischt oder wie hier nur character data "Hello, world!". Sind sie gemischt wie in <p>Das ist ein Paragraph</p>, muss der Parser die markup character von den character data unterscheiden.

If both the external and internal subsets are used, the internal subset is considered to occur before the external subset. This has the effect that entity and attribute-list declarations in the internal subset take precedence over those in the external subset.

2.9 Standalone Document Declaration

Markup declarations can affect the content of the document, as passed from an XML processor to an application; examples are attribute defaults and entity declarations. The standalone document declaration, which may appear as a component of the XML declaration, signals whether or not there are such declarations which appear external to the document entity.

Standalone Document Declaration

[32] SDDeclS ’standalone’ Eq (("’" (’yes’ | ’no’) "’") | (’"’ (’yes’ | ’no’) ’"’)) [ VC: Standalone Document Declaration ]

Sind die delimiter Teil der production, so treten sie in SGML stets mit ihrem Namen auf. In XML treten sie literal in einfache oder doppelte Anführungszeichen eingeschlossen auf, lit als ’"’ und lita als "’". Die Klammer in der obigen rechten Seite der production hieße in SGML (( lita (’yes’ | ’no’) lita) | ( lit (’yes’ | ’no’) lit)).

In a standalone document declaration, the value "yes" indicates that there are no markup declarations external to the document entity (either in the DTD external subset, or in an external parameter entity referenced from the internal subset) which affect the information passed from the XML processor to the application. The value "no" indicates that there are or may be such external markup declarations. Note that the standalone document declaration only denotes the presence of external declarations; the presence, in a document, of references to external entities, when those entities are internally declared, does not change its standalone status.

If there are no external markup declarations, the standalone document declaration has no meaning. If there are external markup declarations but there is no standalone document declaration, the value "no" is assumed.

Any XML document for which standalone="no" holds can be converted algorithmically to a standalone document, which may be desirable for some network delivery applications.

Validity Constraint: Standalone Document Declaration
The standalone document declaration must have the value "no" if any external markup declarations contain declarations of:

An example XML declaration with a standalone document declaration:

<?xml version="1.0" standalone=’yes’?>

2.10 White Space Handling

In editing XML documents, it is often convenient to use "white space" (spaces, tabs, and blank lines, denoted by the nonterminal S in this specification) to set apart the markup for greater readability. Such white space is typically not intended for inclusion in the delivered version of the document. On the other hand, "significant" white space that should be preserved in the delivered version is common, for example in poetry and source code.

An XML processor must always pass all characters in a document that are not markup through to the application. A validating XML processor must also inform the application which of these characters constitute white space appearing in element content.

A special attribute named xml:space may be attached to an element to signal an intention that in that element, white space should be preserved by applications. In valid documents, this attribute, like any other, must be declared if it is used. When declared, it must be given as an enumerated type whose only possible values are "default" and "preserve". For example:

    <!ATTLIST poem   xml:space (default|preserve) ’preserve’>

The value "default" signals that applications’ default white-space processing modes are acceptable for this element; the value "preserve" indicates the intent that applications preserve all the white space. This declared intent is considered to apply to all elements within the content of the element where it is specified, unless overriden with another instance of the xml:space attribute.

The root element of any document is considered to have signaled no intentions as regards application space handling, unless it provides a value for this attribute or the attribute is declared with a default value.

2.11 End-of-Line Handling

XML parsed entities are often stored in computer files which, for editing convenience, are organized into lines. These lines are typically separated by some combination of the characters carriage-return (#xD) and line-feed (#xA).

To simplify the tasks of applications, wherever an external parsed entity or the literal entity value of an internal parsed entity contains either the literal two-character sequence "#xD#xA" or a standalone literal #xD, an XML processor must pass to the application the single character #xA. (This behavior can conveniently be produced by normalizing all line breaks to #xA on input, before parsing.)

2.12 Language Identification

In document processing, it is often useful to identify the natural or formal language in which the content is written. A special attribute named xml:lang may be inserted in documents to specify the language used in the contents and attribute values of any element in an XML document. In valid documents, this attribute, like any other, must be declared if it is used. The values of the attribute are language identifiers as defined by [IETF RFC 1766], "Tags for the Identification of Languages":

Language Identification (2013: Productions 33 through 38 have been removed.)

[33]LanguageID Langcode (’-’ Subcode)* [34]Langcode ISO639CodeIanaCodeUserCode [35]ISO639Code ([a-z] | [A-Z]) ([a-z] | [A-Z]) [36]IanaCode (’i’ | ’I’) ’-’ ([a-z] | [A-Z])+ [37]UserCode (’x’ | ’X’) ’-’ ([a-z] | [A-Z])+ [38] Subcode([a-z] | [A-Z])+

Bei den language codes kann man allenfalls die [33] der [88] von SGML zuordnen, der public text language. Bei dem formal public identifier wird SGML bei HTML in die Lehre gehen müssen, oder HTML die gute Absicht des formal public identifier noch mehr in die Tat umsetzen, als es es mit der URI bereits getan hat.

The Langcode may be any of the following:

There may be any number of Subcode segments; if the first subcode segment exists and the Subcode consists of two letters, then it must be a country code from [ISO 3166], "Codes for the representation of names of countries." If the first subcode consists of more than two letters, it must be a subcode for the language in question registered with IANA, unless the Langcode begins with the prefix "x-" or "X-".

It is customary to give the language code in lower case, and the country code (if any) in upper case. Note that these values, unlike other names in XML documents, are case insensitive.

For example:

<p xml:lang="en">The quick brown fox jumps over the lazy dog.</p>

<p xml:lang="en-GB">What colour is it?</p>

<p xml:lang="en-US">What color is it?</p>

<sp who="Faust" desc=’leise’ xml:lang="de">

<l>Habe nun, ach! Philosophie,</l>

<l>Juristerei, und Medizin</l>

<l>und leider auch Theologie</l>

<l>durchaus studiert mit heißem Bemüh’n.</l>


The intent declared with xml:lang is considered to apply to all attributes and content of the element where it is specified, unless overridden with an instance of xml:lang on another element within that content.

A simple declaration for xml:lang might take the form


but specific default values may also be given, if appropriate. In a collection of French poems for English students, with glosses and notes in English, the xml:lang attribute might be declared this way:

    <!ATTLIST poem   xml:lang NMTOKEN ’fr’>
    <!ATTLIST gloss  xml:lang NMTOKEN ’en’>
    <!ATTLIST note   xml:lang NMTOKEN ’en’>

3. Logical Structures

Each XML document contains one or more elements, the boundaries of which are either delimited by start-tags and end-tags, or, for empty elements, by an empty-element tag. Each element has a type, identified by name, sometimes called its "generic identifier" (GI), and may have a set of attribute specifications. Each attribute specification has a name and a value.


[39]element EmptyElemTagSTag content ETag [ WFC: Element Type Match ] [ VC: Element Valid ]

Die element production stimmt mit der von SGML überein. XML macht zwei element declarations für leere und nicht leere Elemente. In SGML2 oder XML2 wird es bei den Tags nur noch die zwei Regeln ohne Ausnahme geben, dass ein nicht leeres Element einen start-tag und einen end-tag hat und dass ein leeres Element nur einen start-tag hat.

This specification does not constrain the semantics, use, or (beyond syntax) names of the element types and attributes, except that names beginning with a match to ((’X’|’x’)(’M’|’m’)(’L’|’l’)) are reserved for standardization in this or future versions of this specification.

Well-Formedness Constraint: Element Type Match
The Name in an element’s end-tag must match the element type in the start-tag.

Validity Constraint: Element Valid
An element is valid if there is a declaration matching elementdecl where the Name matches the element type, and one of the following holds:

  1. The declaration matches EMPTY and the element has no content.
  2. The declaration matches children and the sequence of child elements belongs to the language generated by the regular expression in the content model, with optional white space (characters matching the nonterminal S) between each pair of child elements.
  3. The declaration matches Mixed and the content consists of character data and child elements whose types match names in the content model.
  4. The declaration matches ANY, and the types of any child elements have been declared.

3.1 Start-Tags, End-Tags, and Empty-Element Tags

The beginning of every non-empty XML element is marked by a start-tag.


[40]STag ’<’ Name (S Attribute)* S? ’>’ [ WFC: Unique Att Spec ] [41]Attribute Name Eq AttValue [ VC: Attribute Value Type ] [ WFC: No < in Attribute Values ]

XML lässt die attribute specification list [31] weg.

The Name in the start- and end-tags gives the element’s type. The Name-AttValue pairs are referred to as the attribute specifications of the element, with the Name in each pair referred to as the attribute name and the content of the AttValue (the text between the or " delimiters) as the attribute value.

Well-Formedness Constraint: Unique Att Spec
No attribute name may appear more than once in the same start-tag or empty-element tag.

Validity Constraint: Attribute Value Type
The attribute must have been declared; the value must be of the type declared for it. (For attribute types, see "3.3 Attribute-List Declarations".)

Well-Formedness Constraint: No External Entity References
Attribute values cannot contain direct or indirect entity references to external entities.

Well-Formedness Constraint: No < in Attribute Values
The replacement text of any entity referred to directly or indirectly in an attribute value (other than "&lt;") must not contain a <.

An example of a start-tag:

<termdef id="dt-dog" term="dog">

The end of every element that begins with a start-tag must be marked by an end-tag containing a name that echoes the element’s type as given in the start-tag:


[42]ETag ’</’ Name S? ’>’

An example of an end-tag:


The text between the start-tag and end-tag is called the element’s content:

Content of Elements

[43]content (elementCharDataReferenceCDSectPIComment)*

Der mixed content und der element content sind in SGML Teile des content. In XML werden der mixed content und der element content auch definiert, treten hier aber als "element | CharData" auf.

If an element is empty, it must be represented either by a start-tag immediately followed by an end-tag or by an empty-element tag. An empty-element tag takes a special form:

Tags for Empty Elements

[44] EmptyElemTag’<’ Name (S Attribute)* S? ’/>’ [ WFC: Unique Att Spec ]

Empty-element tags may be used for any element which has no content, whether or not it is declared using the keyword EMPTY. For interoperability, the empty-element tag must be used, and can only be used, for elements which are declared EMPTY.

Das wird es in Zukunft nicht mehr geben.

Examples of empty elements:

<IMG align="left"

src="http://www.w3.org/Icons/WWW/w3c_home" />



3.2 Element Type Declarations

The element structure of an XML document may, for validation purposes, be constrained using element type and attribute-list declarations. An element type declaration constrains the element’s content.

Element type declarations often constrain which element types can appear as children of the element. At user option, an XML processor may issue a warning when a declaration mentions an element type for which no declaration is provided, but this is not an error.

An element type declaration takes the form:

Element Type Declaration

[45] elementdecl’<!ELEMENT’ S Name S contentspec S? ’>’ [ VC: Unique Element Type Declaration ] [46]contentspec ’EMPTY’ | ’ANY’ | Mixedchildren

where the Name gives the element type being declared.

Die beiden letzen Teile aus contentspec Mixed | children gehören in SGML zum content des element zwischen start-tag und end-tag. Im content ist mixed content alternativ zum element content children erlaubt. Der declared content EMPTY von SGML steht dort in der element declaration. Der Literal ANY ist aus dem content model. Die exceptions aus dem SGML content model gibt es in XML nicht.

Eine Zuweisung von content zur element declaration gibt es in SGML nicht mit Ausnahme des declared content (daher der Name). Ob mixed content oder element content vorliegen, kann der SGML Parser nur anhand von #PCDATA entscheiden. Der SGML parser ist angewiesen, alle content models, bei denen kein #PCDATA ist, als element content aufzufassen (SGML Handbook S. 411f).

where the Name gives the element type being declared.

Validity Constraint: Unique Element Type Declaration
No element type may be declared more than once.

Examples of element type declarations:

br EMPTY p(#PCDATA|emph)* %name.para;%content.para; containerANY>

3.2.1 Element Content

An element type has element content when elements of that type must contain only child elements (no character data), optionally separated by white space (characters matching the nonterminal S). In this case, the constraint includes a content model, a simple grammar governing the allowed types of the child elements and the order in which they are allowed to appear. The grammar is built on content particles (cps), which consist of names, choice lists of content particles, or sequence lists of content particles:

Element-content Models

[47-131]children (choiceseq) (’?’ | ’*’ | ’+’)? [48-128]cp (Namechoiceseq) (’?’ | ’*’ | ’+’)? [49-127.1]choice ’(’ S? cp ( S? ’|’ S? cp )* S? ’)’ [ VC: Proper Group/PE Nesting ] [50-127.2]seq ’(’ S? cp ( S? ’,’ S? cp )* S? ’)’ [ VC: Proper Group/PE Nesting ]

April 2019 XML muss die beiden children choice und seq definieren, weil es keine connectors hat

Entwicklung des content in SGML und XML

SGML XML überall verkürzte Darstellungen
13 element = 24 content 39 element = 43 content 39 = 43
24 content = 25 mixed content | 26 element content 43 content = 39 element 43 = 39
<!ELE = 126 content model <!ELE = 40 contentspec
40 contentspec = 51 Mixed | 47 children
25 mixed content = (48 datachar | 13 element)* 51 Mixed = "#PCDATA" (’|’ Name)* #PCDATA in Mixed
26 element content = 13 element* 47 children = (49 choice | 50 seq) (’?’ | ’*’ | ’+’)? choice und seq w/fehlender connectors erforderlich
126 content model = 127 model group, 138 exceptions? 49 choice = ’(’ S? cp ( S? ’|’ S? cp )* S? ’)’ and wird nicht definiert
50 seq = ’(’ S? cp ( S? ’,’ S? cp )* S? ’)’
127 model group = grpo, 128 content token, (131 connector, 128 content token)*, grpc
128 content token = 129 primitive content token | 127 model group 48 cp = (Name | choice | seq) (’?’ | ’*’ | ’+’)?
129 primitive content token = (rni, ’PCDATA’) | 130 element token #PCDATA im primitive content token
130 element token = 30 GI, 132 occurence indicator?

04/19 In choice und seq werden in XML zwei Dinge zusammengefügt, die in SGML getrennt definiert werden. Einmal legen sie die beiden connectors or und seq aus SGML fest (der connector and entfällt). Zum anderen stellen sie den element content für XML mit cp dar, was in SGML der content token ist. Der primitive content token ganz unten im content model mit #PCDATA fehlt in XML. #PCDATA steht hier ganz oben im 51 Mixed. In 51 Mixed wird eine repeatable or group erzwungen, weil das der einzige Ort ist, in dem #PCDATA auftreten darf, wenn es mit Elementen verbunden ist.


In XML gibt es eine connector1 model group, deren obligatorischer Teil nur aus einem cp besteht: (2013: grpo cp s? or grpc oder wie hier ausgedrückt: ’(’ cp S? ’|’ ’)’, und eine connector2 model group, deren obligatorischer Teil ebenfalls nur aus einem grpo cp grpc besteht, die sich zu der model group mit reinem element content vereinigen mit nachgestellten occurance indicators. Den dritte connector, das and, gibt es in XML nicht.

XML führt die beiden connectors or ’|’ und seq ’,’ als Teile einer group: grpo ( grpc ) ein, ohne die group selbst eingeführt zu haben. Auch besteht der obligatorische Teil der beiden in XML1.0 nur aus einer single group (cp).

Auch kann man einwenden, dass im Endeffekt die Zusammenfügung zweier oder dreier Teile zu einem Ganzen dasselbe ist wie ein in zwei oder drei Teile geteiltes Ganzes. Und der Verzicht auf das and ist nicht schmerzhaft, weil es durch die repeatable or group ersetzt werden kann.

Das ist richtig.

Aber der Fehler im XML Modell besteht im Fehlen des primitive content token als Teil des content token mit mixed content. In XML ist der mixed content nicht Teil des content, sondern direkter Teil der Deklaration. Hier muss entweder das content model von XML korrigiert werden, oder SGML2 entwickelt werden, das an dieser Stelle keiner Änderung bedarf. SGML ist hier ein Geniestreich gelungen, der sich nur schwer in Worte und sicher noch schwerer in Programmzeilen fassen lässt. Das Sicherste für den Programmierer eines guten Parser ist die sture Abbildung des Ineinander der productions von SGML. So kann selbst ein Mensch, der nicht die geringste Ahnung vom Programmieren hat, SGML so abbilden, dass sich alle Teile von SGML ineinander fügen, wie sie sich aufgrund ihrer Physik und Logik fügen müssen (vgl. die Bemerkung unter prd [72]).

In der strict.dtd von html 4.01 hat das W3C etwas Ähnliches gemacht und den body zum element content erklärt. Das hat dort beim Schreiben unter Aufsicht eines Parsers eine Zwangs-Verdopplung des body zur Folge, weil in den body zuerst in ein div element gepackt werden muss, bevor Text eingegeben werden darf.

where each Name is the type of an element which may appear as a child. Any content particle in a choice list may appear in the element content at the location where the choice list appears in the grammar; content particles occurring in a sequence list must each appear in the element content in the order given in the list. The optional character following a name or list governs whether the element or the content particles in the list may occur one or more (+), zero or more (*), or zero or one times (?). The absence of such an operator means that the element or content particle must appear exactly once. This syntax and meaning are identical to those used in the productions in this specification.

The content of an element matches a content model if and only if it is possible to trace out a path through the content model, obeying the sequence, choice, and repetition operators and matching each element in the content against an element type in the content model. For compatibility, it is an error if an element in the document can match more than one occurrence of an element type in the content model. For more information, see "E. Deterministic Content Models".

Die Strenge des if and only if und des rückverfolgbaren Pfades eines jeden Elements, die den XML parser zu einem recht zänkischen Wesen macht, kennt SGML nicht, weil der Autor keine Maschine ist und die Maschine dem Autor zu dienen hat. Vielmehr sucht es die Mitte zwischen der Strenge der Logik und der Freiheit des Wortes so zu formulieren, dass sie auch die Maschine verstehen kann.

Validity Constraint: Proper Group/PE Nesting
Parameter-entity replacement text must be properly nested with parenthetized groups. That is to say, if either of the opening or closing parentheses in a choice, seq, or Mixed construct is contained in the replacement text for a parameter entity, both must be contained in the same replacement text. For interoperability, if a parameter-entity reference appears in a choice, seq, or Mixed construct, its replacement text should not be empty, and neither the first nor last non-blank character of the replacement text should be a connector (| or ,).

Examples of element-content models:

spec (front, body, back?) div1(head, (p | list | note)*, div2*) dictionary-body(%div.mix; | %dict.mix;)*

3.2.2 Mixed Content

An element type has mixed content when elements of that type may contain character data, optionally interspersed with child elements. In this case, the types of the child elements may be constrained, but not their order or their number of occurrences:

Mixed-content Declaration

[51] Mixed’(’ S? ’#PCDATA’ (S? ’|’ S? Name)* S? ’)*’ | ’(’ S? ’#PCDATA’ S? ’)’ [ VC: Proper Group/PE Nesting ] [ VC: No Duplicate Types ]

where the Names give the types of elements that may appear as children.

Validity Constraint: No Duplicate Types
The same name must not appear more than once in a single mixed-content declaration.

Examples of mixed content declarations:

p (#PCDATA|a|ul|b|i|em)* p(#PCDATA | %font; | %phrase; | %special; | %form;)* b(#PCDATA)

Da die parsed character data #PCDATA immer eine unvorhersehbare Folge von Elementen und/oder Text sind, ist (#PCDATA) entweder allein oder in der repeatable or group (#PCDATA |a |b |c| … )* zu Hause, deren Elemente ebenfalls in unvorhersehbarer Anzahl und Reihenfolge auftreten.

3.3 Attribute-List Declarations

Attributes are used to associate name-value pairs with elements. Attribute specifications may appear only within start-tags and empty-element tags; thus, the productions used to recognize them appear in "3.1 Start-Tags, End-Tags, and Empty-Element Tags". Attribute-list declarations may be used:

Attribute-list declarations specify the name, data type, and default value (if any) of each attribute associated with a given element type:

Attribute-list Declaration

[52] AttlistDecl’<!ATTLIST’ S Name AttDef* S? ’>’ [53]AttDef S Name S AttType S DefaultDecl

The Name in the AttlistDecl rule is the type of an element. At user option, an XML processor may issue a warning if attributes are declared for an element type not itself declared, but this is not an error. The Name in the AttDef rule is the name of the attribute.

In DtdEdd heißen die beiden Namen attlistnam (statt associated element type) und AttributeName.

When more than one AttlistDecl is provided for a given element type, the contents of all those provided are merged. When more than one definition is provided for the same attribute of a given element type, the first declaration is binding and later declarations are ignored. For interoperability, writers of DTDs may choose to provide at most one attribute-list declaration for a given element type, at most one attribute definition for a given attribute name, and at least one attribute definition in each attribute-list declaration. For interoperability, an XML processor may at user option issue a warning when more than one attribute-list declaration is provided for a given element type, or more than one attribute definition is provided for a given attribute, but this is not an error.

3.3.1 Attribute Types

XML attribute types are of three kinds: a string type, a set of tokenized types, and enumerated types. The string type may take any literal string as a value; the tokenized types have varying lexical and semantic constraints, as noted:

Attribute Types

[54] AttTypeStringTypeTokenizedTypeEnumeratedType [55]StringType ’CDATA’ [56]TokenizedType ’ID’| ’IDREF’ | ’IDREFS’ | ’ENTITY’ | ’ENTITIES’ | ’NMTOKEN’ | ’NMTOKENS’ [ VC: ID ] [ VC: One ID per Element Type ] [ VC: ID Attribute Default ] [ VC: IDREF ] [ VC: IDREF ] [ VC: Entity Name ] [ VC: Entity Name ] [ VC: Name Token ] [ VC: Name Token ]

Validity Constraint: ID
Values of type ID must match the Name production. A name must not appear more than once in an XML document as a value of this type; i.e., ID values must uniquely identify the elements which bear them.

Validity Constraint: One ID per Element Type
No element type may have more than one ID attribute specified.

Validity Constraint: ID Attribute Default
An ID attribute must have a declared default of #IMPLIED or #REQUIRED.

Validity Constraint: IDREF
Values of type IDREF must match the Name production, and values of type IDREFS must match Names; each Name must match the value of an ID attribute on some element in the XML document; i.e. IDREF values must match the value of some ID attribute.

Validity Constraint: Entity Name
Values of type ENTITY must match the Name production, values of type ENTITIES must match Names; each Name must match the name of an unparsed entity declared in the DTD.

Validity Constraint: Name Token
Values of type NMTOKEN must match the Nmtoken production; values of type NMTOKENS must match Nmtokens.

Enumerated attributes can take one of a list of values provided in the declaration. There are two kinds of enumerated types:

Enumerated Attribute Types

[57] EnumeratedTypeNotationTypeEnumeration [58]NotationType ’NOTATION’ S ’(’ S? Name (S? ’|’ S? Name)* S? ’)’ [ VC: Notation Attributes ] [59]Enumeration ’(’ S? Nmtoken (S? ’|’ S? Nmtoken)* S? ’)’ [ VC: Enumeration ]

A NOTATION attribute identifies a notation, declared in the DTD with associated system and/or public identifiers, to be used in interpreting the element to which the attribute is attached.

Validity Constraint: Notation Attributes
Values of this type must match one of the notation names included in the declaration; all notation names in the declaration must be declared.

Validity Constraint: Enumeration
Values of this type must match one of the Nmtoken tokens in the declaration.

For interoperability, the same Nmtoken should not occur more than once in the enumerated attribute types of a single element type.

3.3.2 Attribute Defaults

An attribute declaration provides information on whether the attribute’s presence is required, and if not, how an XML processor should react if a declared attribute is absent in a document.

Attribute Defaults

[60]DefaultDecl ’#REQUIRED’ | ’#IMPLIED’| ((’#FIXED’ S)? AttValue) [ VC: Required Attribute ] [ VC: Attribute Default Legal ] [ WFC: No < in Attribute Values ] [ WFC: No < in Attribute Values ] [ VC: Fixed Attribute Default ]

In an attribute declaration, #REQUIRED means that the attribute must always be provided, #IMPLIED that no default value is provided. If the declaration is neither #REQUIRED nor #IMPLIED, then the AttValue value contains the declared default value; the #FIXED keyword states that the attribute must always have the default value. If a default value is declared, when an XML processor encounters an omitted attribute, it is to behave as though the attribute were present with the declared default value.

Validity Constraint: Required Attribute
If the default declaration is the keyword #REQUIRED, then the attribute must be specified for all elements of the type in the attribute-list declaration.

Validity Constraint: Attribute Default Legal
The declared default value must meet the lexical constraints of the declared attribute type.

Validity Constraint: Fixed Attribute Default
If an attribute has a default value declared with the #FIXED keyword, instances of that attribute must match the default value.

Examples of attribute-list declarations:

termdef idID name list type bullets|ordered|glossary "ordered" form method "POST"

3.3.3 Attribute-Value Normalization

Before the value of an attribute is passed to the application or checked for validity, the XML processor must normalize it as follows:

If the declared value is not CDATA, then the XML processor must further process the normalized attribute value by discarding any leading and trailing space (#x20) characters, and by replacing sequences of space (#x20) characters by a single space (#x20) character.

All attributes for which no declaration has been read should be treated by a non-validating parser as if declared CDATA.

3.4 Conditional Sections

Conditional sections are portions of the document type declaration external subset which are included in, or excluded from, the logical structure of the DTD based on the keyword which governs them.

Conditional Section

[61]conditionalSect includeSectignoreSect [62]includeSect ’<![’ S? ’INCLUDE’ S? ’[’ extSubsetDecl ’]]>’ [63]ignoreSect ’<![’ S? ’IGNORE’ S? ’[’ ignoreSectContents* ’]]>’ [64]ignoreSectContents Ignore (’<![’ ignoreSectContents ’]]>’ Ignore)* [65] IgnoreChar* - (Char* (’<![’ | ’]]>’) Char*)

Wie in 2.7 erwähnt, ist die conditional section nur eine Form der marked section mit den keywords INCLUDE und IGNORE und entsprechenden Anforderungen an den Rechner. Das Ineinander (nesting) ist in SGML nur in den marked sections mit den keywords CDATA und RCDATA nicht möglich, weil dort das markup nicht erkannt wird (SGML Handbook S. 394). Warum die include section in XML auf markup declarations beschränkt ist, ist nicht ganz klar. In SGML gelten die sections für beliebige Dokumententeile.

Like the internal and external DTD subsets, a conditional section may contain one or more complete declarations, comments, processing instructions, or nested conditional sections, intermingled with white space.

If the keyword of the conditional section is INCLUDE, then the contents of the conditional section are part of the DTD. If the keyword of the conditional section is IGNORE, then the contents of the conditional section are not logically part of the DTD. Note that for reliable parsing, the contents of even ignored conditional sections must be read in order to detect nested conditional sections and ensure that the end of the outermost (ignored) conditional section is properly detected. If a conditional section with a keyword of INCLUDE occurs within a larger conditional section with a keyword of IGNORE, both the outer and the inner conditional sections are ignored.

If the keyword of the conditional section is a parameter-entity reference, the parameter entity must be replaced by its content before the processor decides whether to include or ignore the conditional section.

An example:

draft INCLUDE final IGNORE %draft; book (comments*, title, body, supplements?) %final; book (title, body, supplements?)

Wie im Quelltext der Deklarationen zu sehen ist, der der SGML Vorlage nachgebildet ist, entscheidet allein die status keyword specification darüber, um was für eine marked section es sich handelt. Auch das Beispiel mit der parameter entity reference an der Stelle des keywords weist darauf hin, dass es nicht verschiedene Arten von marked sections gibt, sondern eine marked section, die verschiedenen Aufgaben nachkommt.

Marked sections stellen in SGML keine Bedingungen, was in sie rein darf und was nicht, außer der physikalischen oder logischen, wie man will, dass sie nicht mitten in einem Teil aufhören können, dessen Anfang in ihnen ist. Ihr content oben in DtdEdd ist einer der wenigen Fälle, in denen ANY angebracht ist. ANY bedeutet, alle in der vorliegenden DTD erlaubten Elemente in beliebiger Anzahl und Folge.

4. Physical Structures

An XML document may consist of one or many storage units. These are called entities; they all have content and are all (except for the document entity, see below, and the external DTD subset) identified by name. Each XML document has one entity called the document entity, which serves as the starting point for the XML processor and may contain the whole document.

Entities may be either parsed or unparsed. A parsed entity’s contents are referred to as its replacement text; this text is considered an integral part of the document.

An unparsed entity is a resource whose contents may or may not be text, and if text, may not be XML. Each unparsed entity has an associated notation, identified by name. Beyond a requirement that an XML processor make the identifiers for the entity and notation available to the application, XML places no constraints on the contents of unparsed entities.

Parsed entities are invoked by name using entity references; unparsed entities by name, given in the value of ENTITY or ENTITIES attributes.

General entities are entities for use within the document content. In this specification, general entities are sometimes referred to with the unqualified term entity when this leads to no ambiguity. Parameter entities are parsed entities for use within the DTD. These two types of entities use different forms of reference and are recognized in different contexts. Furthermore, they occupy different namespaces; a parameter entity and a general entity with the same name are two distinct entities.

4.1 Character and Entity References

A character reference refers to a specific character in the ISO/IEC 10646 character set, for example one not directly accessible from available input devices.

Character Reference

[66]CharRef ’&#’ [0-9]+ ’;’ | ’&#x’ [0-9a-fA-F]+ ’;’ [ WFC: Legal Character ]

Well-Formedness Constraint: Legal Character
Characters referred to using character references must match the production for Char.

If the character reference begins with "&#x", the digits and letters up to the terminating ; provide a hexadecimal representation of the character’s code point in ISO/IEC 10646. If it begins just with "&#", the digits up to the terminating ; provide a decimal representation of the character’s code point.

Die beiden references müssen in SGML zwei productions sein, weil sie zwei verschiedene delimiter cro, character reference open und hcro, hexadecimal character reference open haben und Alternativen wie (cro|hcro) nicht vorgesehen sind.

An entity reference refers to the content of a named entity. References to parsed general entities use ampersand (&) and semicolon (;) as delimiters. Parameter-entity references use percent-sign (%) and semicolon (;) as delimiters.

Entity Reference

[67] ReferenceEntityRefCharRef

Eine gemeinsame production für die entity reference und die character reference kann es nicht geben, weil die entity deklariert wird, während die character außerhalb von SGML oder XML ihre Nummern erhalten, daher nicht deklariert werden können. Die character references gelten "ungefragt" immer für das gerade vorliegende character set.

[68]EntityRef ’&’ Name ’;’ [ VC: Entity Declared ] [ WFC: Parsed Entity ] [ WFC: No Recursion ] [69]PEReference ’%’ Name ’;’ [ VC: Entity Declared ] [ WFC: No Recursion ] [ WFC: In DTD ]

Well-Formedness Constraint: Entity Declared
In a document without any DTD, a document with only an internal DTD subset which contains no parameter entity references, or a document with "standalone=’yes’", the Name given in the entity reference must match that in an entity declaration, except that well-formed documents need not declare any of the following entities: amp, lt, gt, apos (rsquo), quot. The declaration of a parameter entity must precede any reference to it. Similarly, the declaration of a general entity must precede any reference to it which appears in a default value in an attribute-list declaration. Note that if entities are declared in the external subset or in external parameter entities, a non-validating processor is not obligated to read and process their declarations; for such documents, the rule that an entity must be declared is a well-formedness constraint only if standalone=’yes’.

Die general entity trüge ihren Namen nicht zu Recht, wenn sie wie die character reference nur Buchstaben repräsentieren könnte. In SGML ist eine entity definiert als eine "collection of characters that can be referenced as a unit". Die character entity ist nur die kleinstmögliche Form einer general entity, die ein Buchstabe, ein Satz oder ein Roman sein kann. Eine character data entity wie beta ist dort eine SDATA entity, für die SGML keine Verantwortung trägt, vielmehr dem System überlässt, für &beta; das Richtige: β einzusetzen.

Validity Constraint: Entity Declared
In a document with an external subset or external parameter entities with "standalone=’no’", the Name given in the entity reference must match that in an entity declaration. For interoperability, valid documents should declare the entities amp, lt, gt, apos (rsquo), quot, in the form specified in "4.6 Predefined Entities". The declaration of a parameter entity must precede any reference to it. Similarly, the declaration of a general entity must precede any reference to it which appears in a default value in an attribute-list declaration.

Well-Formedness Constraint: Parsed Entity
An entity reference must not contain the name of an unparsed entity. Unparsed entities may be referred to only in attribute values declared to be of type ENTITY or ENTITIES.

Well-Formedness Constraint: No Recursion
A parsed entity must not contain a recursive reference to itself, either directly or indirectly.

Well-Formedness Constraint: In DTD
Parameter-entity references may only appear in the DTD.

Examples of character and entity references:

Type <key>less-than</key> (&#x3C;) to save options.

This document was prepared on &docdate; and

is classified &security-level;.

Example of a parameter-entity reference:

<!-- declare the parameter entity "ISOLat2"... -->

ISOLat2 http://www.xml.com/iso/isolat2-xml.entities

<!-- ... now reference it. -->


4.2 Entity Declarations

Entities are declared thus:

Entity Declaration

[70]EntityDecl GEDeclPEDecl [71]GEDecl ’<!ENTITY’ S Name S EntityDef S? ’>’ [72]PEDecl ’<!ENTITY’ S ’%’ S Name S PEDef S? ’>’

Auch in SGML ist die entity das Ganze, aber die beiden Teile werden durch die entity names festgelegt. In DtdEdd bin ich gewissermaßen dem Beispiel von XML gefolgt und habe zwei entity Arten, weil das das Schreiben der DTD vereinfacht.

Für ein Unternehmen wie SGML ist der Weg des Ganzen, das sich in Teile teilt, der weitaus überlegenere. Als Beleg für diese Behauptung habe ich eine SGML2.dtd geschrieben (alt:TG_C_Prd_Ent_DTD.fm, noch nicht geTURBLEd. neu: ../SG/dtd.html), die aus nichts anderem besteht als aus der Abschrift der Productions, nur nicht mit <!PRD, sondern mit <!ELEMENT am Anfang. Das Ergebnis ist, dass sich jeder einzelne Teil, also die um rund ein Viertel verringerten 200 productions in der ersten production ineinander fügen, so, dass man den theoretischen Gesamtaufbau eines SGML document von der [1] bis zum einzelnen character genau studieren kann. Zwar ist das jedem SGML Studenten klar, aber die Gewissheit einerseits und es vor Augen zu sehen, sind Zweierlei.

Das Schreiben einer XML.dtd, mit der man den Aufbau von XML studieren kann, ist mit den XML productions in ihrer derzeitigen Form undenkbar.

[73]EntityDef EntityValue | (ExternalID NDataDecl?) [74]PEDef EntityValueExternalID

Wie die entity, so ist auch der entity text in XML zweigeteilt.

The Name identifies the entity in an entity reference or, in the case of an unparsed entity, in the value of an ENTITY or ENTITIES attribute. If the same entity is declared more than once, the first declaration encountered is binding; at user option, an XML processor may issue a warning if entities are declared multiple times.

4.2.1 Internal Entities

If the entity definition is an EntityValue, the defined entity is called an internal entity. There is no separate physical storage object, and the content of the entity is given in the declaration. Note that some processing of entity and character references in the literal entity value may be required to produce the correct replacement text: see "4.5 Construction of Internal Entity Replacement Text".

An internal entity is a parsed entity.

Example of an internal entity declaration:

Pub-Status"This is a pre-release of the specification."

4.2.2 External Entities

If the entity is not internal, it is an external entity, declared as follows:

External Entity Declaration

[75]ExternalID ’SYSTEM’ S SystemLiteral| ’PUBLIC’ S PubidLiteral S SystemLiteral [76]NDataDecl S ’NDATA’ S Name [ VC: Notation Declared ]

If the NDataDecl is present, this is a general unparsed entity; otherwise it is a parsed entity.

Validity Constraint: Notation Declared
The Name must match the declared name of a notation.

The SystemLiteral is called the entity’s system identifier. It is a URI, which may be used to retrieve the entity. Note that the hash mark (#) and fragment identifier frequently used with URIs are not, formally, part of the URI itself; an XML processor may signal an error if a fragment identifier is given as part of a system identifier. Unless otherwise provided by information outside the scope of this specification (e.g. a special XML element type defined by a particular DTD, or a processing instruction defined by a particular application specification), relative URIs are relative to the location of the resource within which the entity declaration occurs. A URI might thus be relative to the document entity, to the entity containing the external DTD subset, or to some other external parameter entity.

An XML processor should handle a non-ASCII character in a URI by representing the character in UTF-8 as one or more bytes, and then escaping these bytes with the URI escaping mechanism (i.e., by converting each byte to %HH, where HH is the hexadecimal notation of the byte value).

In addition to a system identifier, an external identifier may include a public identifier. An XML processor attempting to retrieve the entity’s content may use the public identifier to try to generate an alternative URI. If the processor is unable to do so, it must use the URI specified in the system literal. Before a match is attempted, all strings of white space in the public identifier must be normalized to single space characters (#x20), and leading and trailing white space must be removed.

Die Autoren geben dem system identifier Vorrang vor dem public identifier. Dem ist beizupflichten, weil ich von einer DTD in meinem System weiß, wie sie in den Arbeitsspeicher kommt. Das weiß ich von den public identifiern in der derzeitigen publicity nicht.

Examples of external entity declarations:

open-hatch http://www.textuality.com/boilerplate/OpenHatch.xml open-hatch -//Textuality//TEXT Standard open-hatch boilerplate//EN http://www.textuality.com/boilerplate/OpenHatch.xml hatch-pic ../grafix/OpenHatch.gif gif

DtdEdd ist korrigiert, so dass der Absatz nicht mehr gilt: Bei dem system identifier im ersten Beispiel und bei der "NDATA" entity habe ich ein wenig gemogelt, wie man im Quelltext sieht.Im ersten Fall habe ich statt des SystemIdentifiers den den DeclarationPartLiteral genommen und beim notation name von hatch-pic "gif" in das html401 element ins hineingeschrieben. Das liegt daran, dass ich mit den Notations noch zu wenig vertraut bin, um sie mit Verstand in DtdEdd zu integrieren. Und im anderen Fall liegt es nicht in meiner Hand, den public identifier fakultativ zu machen, so dass bei einem leeren public identifier dessen delimiter "" (lit lit) da stehen. SGML2 sollte den public identifier fakultativ machen. Er hat sich sowieso schon stets nur aufgebläht, ohne etwas zum Inhalt beizutragen. Er ist fakultativ, du hast es nur nicht begriffen.

4.3 Parsed Entities

4.3.1 The Text Declaration

External parsed entities may each begin with a text declaration.

Text Declaration

[77] TextDecl’<?xml’ VersionInfo? EncodingDecl S? ’?>’

The text declaration must be provided literally, not by reference to a parsed entity. No text declaration may appear at any position other than the beginning of an external parsed entity.

4.3.2 Well-Formed Parsed Entities

The document entity is well-formed if it matches the production labeled document. An external general parsed entity is well-formed if it matches the production labeled extParsedEnt. An external parameter entity is well-formed if it matches the production labeled extPE.

Well-Formed External Parsed Entity

[78]extParsedEnt TextDecl? content

Die erste production von XML hat keinen Ort für eine XML text entity, die sich in das document einfügt. Daher muss der external parsed entity die TextDecl mitgeteilt werden. In SGML befindet sich die SGML text entity in der ersten production, so dass dort solche Mitteilungen überflüssig sind.

[79]extPE TextDecl? extSubsetDecl

An internal general parsed entity is well-formed if its replacement text matches the production labeled content. All internal parameter entities are well-formed by definition.

A consequence of well-formedness in entities is that the logical and physical structures in an XML document are properly nested; no start-tag, end-tag, empty-element tag, element, comment, processing instruction, character reference, or entity reference can begin in one entity and end in another.

Der Logik ist das Ineinander des Nesting von entities so lieb wie das Ineinander des teilehabenden ganzen Element. Für sie ist es nur ein von links nach rechts lesen oder ein von rechts nach links lesen. Mal steht das Ganze im Anfang, mal der Teil. Tatsächlich ist auf der Deklarationsebene eine Beziehung des Durchschnitts zweier Elemente nicht möglich. Hier sind zwei Elemente immer entweder ineinander oder nebeneinander. Aber tolerante Parser wie der html Parser, der Browser, lassen sie im markup zu, etwa normal<i>kursiv<b>kursiv und fett</i>nur fett</b>normal. Dort müssen sie aber manuell eingegeben werden. Beim Reimport der XML.html in den SGML Editor geht der Durchschnitt verloren. Wie hier auf der unteren Ebene so ist auch auf der Ebene der Beziehungen mehrerer DTDs zueinander ein Durchschnitt möglich. So hat WT einen Durchschnitt mit HT. Das zeigt wieder nur, dass sich die Gesetze des Ganzen und des Teils über unsere Vorschriften hinwegsetzen, weil sie universell sind im Sinne des Wortes.

Die letzten productions zeigen entweder, dass in XML etwas nachzuholen ist, oder sie sind ein Hinweis darauf, dass der Umgang mit XML text entities gemäß der 123 Methode am Ende und nicht gemäß der ABC Methode am Anfang zu erfolgen hat. Das kann erst nach weiteren Forschungen über die Beziehungen zwischen SGML und XML gesagt werden.

4.3.3 Character Encoding in Entities

Each external parsed entity in an XML document may use a different encoding for its characters. All XML processors must be able to read entities in either UTF-8 or UTF-16.

Entities encoded in UTF-16 must begin with the Byte Order Mark described by ISO/IEC 10646 Annex E and Unicode Appendix B (the ZERO WIDTH NO-BREAK SPACE character, #xFEFF). This is an encoding signature, not part of either the markup or the character data of the XML document. XML processors must be able to use this character to differentiate between UTF-8 and UTF-16 encoded documents.

Although an XML processor is required to read only entities in the UTF-8 and UTF-16 encodings, it is recognized that other encodings are used around the world, and it may be desired for XML processors to read entities that use them. Parsed entities which are stored in an encoding other than UTF-8 or UTF-16 must begin with a text declaration containing an encoding declaration:

Encoding Declaration

[80]EncodingDecl S ’encoding’ Eq (’"’ EncName ’"’ |  "’" EncName "’" ) [81] EncName[A-Za-z] ([A-Za-z0-9._] | ’-’)* Encoding name contains only Latin characters

In the document entity, the encoding declaration is part of the XML declaration. The EncName is the name of the encoding used.

In an encoding declaration, the values "UTF-8", "UTF-16", "ISO-10646-UCS-2", and "ISO-10646-UCS-4" should be used for the various encodings and transformations of Unicode / ISO/IEC 10646, the values "ISO-8859-1", "ISO-8859-2", ... "ISO-8859-9" should be used for the parts of ISO 8859, and the values "ISO-2022-JP", "Shift_JIS", and "EUC-JP" should be used for the various encoded forms of JIS X-0208-1997. XML processors may recognize other encodings; it is recommended that character encodings registered (as charsets) with the Internet Assigned Numbers Authority [IANA], other than those just listed, should be referred to using their registered names. Note that these registered names are defined to be case-insensitive, so processors wishing to match against them should do so in a case-insensitive way.

In the absence of information provided by an external transport protocol (e.g. HTTP or MIME), it is an error for an entity including an encoding declaration to be presented to the XML processor in an encoding other than that named in the declaration, for an encoding declaration to occur other than at the beginning of an external entity, or for an entity which begins with neither a Byte Order Mark nor an encoding declaration to use an encoding other than UTF-8. Note that since ASCII is a subset of UTF-8, ordinary ASCII entities do not strictly need an encoding declaration.

It is a fatal error when an XML processor encounters an entity with an encoding that it is unable to process.

Examples of encoding declarations:

<?xml encoding=’UTF-8’?>

<?xml encoding=’EUC-JP’?>

4.4 XML Processor Treatment of Entities and References

The table below summarizes the contexts in which character references, entity references, and invocations of unparsed entities might appear and the required behavior of an XML processor in each case. The labels in the leftmost column describe the recognition context:

Reference in Content
as a reference anywhere after the start-tag and before the end-tag of an element; corresponds to the nonterminal content.
Reference in Attribute Value
as a reference within either the value of an attribute in a start-tag, or a default value in an attribute declaration; corresponds to the nonterminal AttValue.
Occurs as Attribute Value
as a Name, not a reference, appearing either as the value of an attribute which has been declared as type ENTITY, or as one of the space-separated tokens in the value of an attribute which has been declared as type ENTITIES.
Reference in Entity Value
as a reference within a parameter or internal entity’s literal entity value in the entity’s declaration; corresponds to the nonterminal EntityValue.
Reference in DTD
as a reference within either the internal or external subsets of the DTD, but outside of an EntityValue or AttValue.
Entity Type Character
Parameter Internal
External Parsed
in Content
Not recognized Included Included if validating Forbidden Included
in Attribute Value
Not recognized Included in literal Forbidden Forbidden Included
Occurs as
Attribute Value
Not recognized Forbidden Forbidden Notify Not recognized
in EntityValue
Included in literal Bypassed Bypassed Forbidden Included
in DTD
Included as PE Forbidden Forbidden Forbidden Forbidden

4.4.1 Not Recognized

Outside the DTD, the % character has no special significance; thus, what would be parameter entity references in the DTD are not recognized as markup in content. Similarly, the names of unparsed entities are not recognized except when they appear in the value of an appropriately declared attribute.

4.4.2 Included

An entity is included when its replacement text is retrieved and processed, in place of the reference itself, as though it were part of the document at the location the reference was recognized. The replacement text may contain both character data and (except for parameter entities) markup, which must be recognized in the usual way, except that the replacement text of entities used to escape markup delimiters (the entities amp, lt, gt, apos (rsquo), quot) is always treated as data. (The string "AT&amp;T;" expands to "AT&T;" and the remaining ampersand is not recognized as an entity-reference delimiter.) A character reference is included when the indicated character is processed in place of the reference itself.

4.4.3 Included If Validating

When an XML processor recognizes a reference to a parsed entity, in order to validate the document, the processor must include its replacement text. If the entity is external, and the processor is not attempting to validate the XML document, the processor may, but need not, include the entity’s replacement text. If a non-validating parser does not include the replacement text, it must inform the application that it recognized, but did not read, the entity.

This rule is based on the recognition that the automatic inclusion provided by the SGML and XML entity mechanism, primarily designed to support modularity in authoring, is not necessarily appropriate for other applications, in particular document browsing. Browsers, for example, when encountering an external parsed entity reference, might choose to provide a visual indication of the entity’s presence and retrieve it for display only on demand.

"Externe entities", die der Browser kennt, sind Bilder oder iframes. Mit general entities, die einen html text samt markup an die Stelle des Aufrufs etwa von &html-fragment; setzt, kann der Browser nichts anfangen. Das kann auch FrameMaker mit SGML text entities nicht. Es kann nur eine Menge externer SGML text entities im book Mechanismus zu einer Einheit zusammenfassen.

Mit anderen Worten: Es gibt keine XML text entities als formale Bestandteile von XML. Die kann es nicht geben, weil die erste production von XML nach der Definition der SGML text entities beginnt.

4.4.4 Forbidden

The following are forbidden, and constitute fatal errors:

4.4.5 Included in Literal

When an entity reference appears in an attribute value, or a parameter entity reference appears in a literal entity value, its replacement text is processed in place of the reference itself as though it were part of the document at the location the reference was recognized, except that a single or double quote character in the replacement text is always treated as a normal data character and will not terminate the literal. For example, this is well-formed:

<!ENTITY % YN ’"Yes"’ >

<!ENTITY WhatHeSaid "He said &YN;" >

while this is not:

<!ENTITY EndAttr "27’" >

<element attribute=’a-&EndAttr;>

4.4.6 Notify

When the name of an unparsed entity appears as a token in the value of an attribute of declared type ENTITY or ENTITIES, a validating processor must inform the application of the system and public (if any) identifiers for both the entity and its associated notation.

4.4.7 Bypassed

When a general entity reference appears in the EntityValue in an entity declaration, it is bypassed and left as is.

4.4.8 Included as PE

Just as with external parsed entities, parameter entities need only be included if validating. When a parameter-entity reference is recognized in the DTD and included, its replacement text is enlarged by the attachment of one leading and one following space (#x20) character; the intent is to constrain the replacement text of parameter entities to contain an integral number of grammatical tokens in the DTD.

4.5 Construction of Internal Entity Replacement Text

In discussing the treatment of internal entities, it is useful to distinguish two forms of the entity’s value. The literal entity value is the quoted string actually present in the entity declaration, corresponding to the non-terminal EntityValue. The replacement text is the content of the entity, after replacement of character references and parameter-entity references.

The literal entity value as given in an internal entity declaration (EntityValue) may contain character, parameter-entity, and general-entity references. Such references must be contained entirely within the literal entity value. The actual replacement text that is included as described above must contain the replacement text of any parameter entities referred to, and must contain the character referred to, in place of any character references in the literal entity value; however, general-entity references must be left as-is, unexpanded. For example, given the following declarations:

<!ENTITY % pub "&#xc9;ditions Gallimard" >

<!ENTITY rights "All rights reserved" >

<!ENTITY book "La Peste: Albert Camus,

&#xA9; 1947 %pub;. &rights;" >

then the replacement text for the entity "book" is:

La Peste: Albert Camus,

© 1947 Éditions Gallimard. &rights;

The general-entity reference "&rights;" would be expanded should the reference "&book;" appear in the document’s content or an attribute value.

Du kannst die entity rights als CDATA entity mit dem entity text "Alle Rechte usw." in der isoall.ent deklarieren, damit in die HT DTD einbinden und als &rights; im Text eingefügen. Der Browser gibt im markup zwar eine general entity reference aus, aber immer nur als &, gefolgt von rights gefolgt von ; , weil er diese entity nicht wie &reg; als ® eingespeichert hat.

These simple rules may have complex interactions; for a detailed discussion of a difficult example, see "D. Expansion of Entity and Character References".

4.6 Predefined Entities

Entity and character references can both be used to escape the left angle brakket, ampersand, and other delimiters. A set of general entities (amp, lt, gt, apos(rsquo), quot) is specified for this purpose. Numeric character references may also be used; they are expanded immediately when recognized and must be treated as character data, so the numeric character references "&#60;" and "&#38;" may be used to escape < and & when they occur in character data.

All XML processors must recognize these entities whether they are declared or not. For interoperability, valid XML documents should declare these entities, like any others, before using them. If the entities in question are declared, they must be declared as internal entities whose replacement text is the single character being escaped or a character reference to that character, as shown below.

<!ENTITY lt "&#38;#60;">

<!ENTITY gt "&#62;">

<!ENTITY amp "&#38;#38;">

<!ENTITY apos "&#39;">

<!ENTITY quot "&#34;">

Sowohl FrameMaker7.2 als auch HTML4.01 haben vergessen, apos (=lita delimiter) in ihre entity Sammlungen bzw, ihre Lese- und Schreibregeln aufzunehmen. Das hat zur Folge, dass &apos; in der letzten vorhandenen SGML Software (James Clark’s open source SGML parser nicht vergessen! Er ist aber nicht zum Lernen von SGML geeignet.) nicht round-trip-tauglich ist und daher in der vorliegenden Dokumentation nicht verwendet werden kann. Dagegen ist rsquo sowohl in HTML4.01: <!ENTITY rsquo CDATA "&#8217;" -- right single quotation mark--, auch in FrameMaker7.2 als SDATA entity verwendbar. Das ist zwar typographisch nicht ganz in Ordnung, erfüllt aber seinen Zweck. Die Nummer 8217 interessiert den SGML Parser nicht (Daher kann der entity text leer "" sein.), nur der Name rsquo und die Herkunft aus einem der ISO entity sets. In der html401 Dokumentation von XML wird daher anstelle von apos rsquo verwendet.

Dass sich das erledigt hat, steht schon oben. Aber da ich den Grund nicht begreife, lasse ich es doppelt stehen.

Note that the < and & characters in the declarations of "lt" and "amp" are doubly escaped to meet the requirement that entity replacement be well-formed.

4.7 Notation Declarations

Notations identify by name the format of unparsed entities, the format of elements which bear a notation attribute, or the application to which a processing instruction is addressed.

Notation declarations provide a name for the notation, for use in entity and attribute-list declarations and in attribute specifications, and an external identifier for the notation which may allow an XML processor or its client application to locate a helper application capable of processing data in the given notation.

Notation Declarations

[82] NotationDecl’<!NOTATION’ S Name S (ExternalIDPublicID) S? ’>’ [83]PublicID ’PUBLIC’ S PubidLiteral

XML processors must provide applications with the name and external identifier(s) of any notation declared and referred to in an attribute value, attribute definition, or entity declaration. They may additionally resolve the external identifier into the system identifier, file name, or other information needed to allow the application to call a processor for data in the notation described. (It is not an error, however, for XML documents to declare and refer to notations for which notation-specific applications are not available on the system where the XML processor or application is running.)

4.8 Document Entity

The document entity serves as the root of the entity tree and a starting-point for an XML processor. This specification does not specify how the document entity is to be located by an XML processor; unlike other entities, the document entity has no name and might well appear on a processor input stream without any identification at all.

Der XML production [1] document entspricht die SGML production [2] SGML document entity. Sie ist dort auch namenlos.

5. Conformance

5.1 Validating and Non-Validating Processors

Conforming XML processors fall into two classes: validating and non-validating.

Validating and non-validating processors alike must report violations of this specification’s well-formedness constraints in the content of the document entity and any other parsed entities that they read.

Validating processors must report violations of the constraints expressed by the declarations in the DTD, and failures to fulfill the validity constraints given in this specification. To accomplish this, validating XML processors must read and process the entire DTD and all external parsed entities referenced in the document.

Non-validating processors are required to check only the document entity, including the entire internal DTD subset, for well-formedness. While they are not required to check the document for validity, they are required to process all the declarations they read in the internal DTD subset and in any parameter entity that they read, up to the first reference to a parameter entity that they do not read; that is to say, they must use the information in those declarations to normalize attribute values, include the replacement text of internal entities, and supply default attribute values. They must not process entity declarations or attribute-list declarations encountered after a reference to a parameter entity that is not read, since the entity may have contained overriding declarations.

5.2 Using XML Processors

The behavior of a validating XML processor is highly predictable; it must read every piece of a document and report all well-formedness and validity violations. Less is required of a non-validating processor; it need not read any part of the document other than the document entity. This has two effects that may be important to users of XML processors:

For maximum reliability in interoperating between different XML processors, applications which use non-validating processors should not rely on any behaviors not required of such processors. Applications which require facilities such as the use of default attributes or internal entities which are declared in external entities should use validating XML processors.

6. Notation

The formal grammar of XML is given in this specification using a simple Extended Backus-Naur Form (EBNF) notation. Each rule in the grammar defines one symbol, in the form

symbol ::= expression

In der vorliegenden Notation mit <!PRD ist kein sichtbares Zuordnungszeichen von linker zu rechter Seite der Definitionsgleichung (::=), dafür hat der DtdPart zwischen dem prdnam und dem DeclaredContent das is element, so dass sich die Production liest "prdnam is DeclaredContent". Der Name DeclaredContent erklärt sich dadurch, dass in DtdEdd für die rechte Seite nur die beiden Behälter ContentModel oder DeclaredContent zur Verfügung stehen, das ContentModel aber im Editor stets in einer model group ist, während die Definitionen von XML ohne Klammern sind.

Symbols are written with an initial capital letter if they are defined by a regular expression, or with an initial lower case letter otherwise. Literal strings are quoted.

Within the expression on the right-hand side of a rule, the following expressions are used to match strings of one or more characters:

where N is a hexadecimal integer, the expression matches the character in ISO/IEC 10646 whose canonical (UCS-4) code value, when interpreted as an unsigned binary number, has the value indicated. The number of leading zeros in the #xN form is insignificant; the number of leading zeros in the corresponding code value is governed by the character encoding in use and is not significant for XML.
[a-zA-Z], [#xN-#xN]
matches any character with a value in the range(s) indicated (inclusive).
[^a-z], [^#xN-#xN]
matches any character with a value outside the range indicated.
[^abc], [^#xN#xN#xN]
matches any character with a value not among the characters given.
matches a literal string matching that given inside the double quotes.
matches a literal string matching that given inside the single quotes.

These symbols may be combined to match more complex patterns as follows, where A and B represent simple expressions:

expression is treated as a unit and may be combined as described in this list.
matches A or nothing; optional A.
matches A followed by B.
A | B
matches A or B but not both.
A - B
matches any string that matches A but does not match B.
matches one or more occurrences of A.
matches zero or more occurrences of A.

Other notations used in the productions are:

/* ... */
[ wfc: ... ]
well-formedness constraint; this identifies by name a constraint on well-formed documents associated with a production.
[ vc: ... ]
validity constraint; this identifies by name a constraint on valid documents associated with a production.
A - B
ist in SGML nicht möglich. Dafür gibt es dort
A & B
das in XML nicht möglich ist. Es bedeutet A und B, beide genau einmal, in beliebiger Reihenfolge.


A. References

A.1 Normative References

(Internet Assigned Numbers Authority) Official Names for Character Sets, ed. Keld Simonsen et al. See ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets.
IETF (Internet Engineering Task Force). RFC 1766: Tags for the Identification of Languages, ed. H. Alvestrand. 1995.
ISO 639
(International Organization for Standardization). ISO 639:1988 (E). Code for the representation of names of languages. [Geneva]: International Organization for Standardization, 1988.
ISO 3166
(International Organization for Standardization). ISO 3166-1:1997 (E). Codes for the representation of names of countries and their subdivisions -- Part 1: Country codes [Geneva]: International Organization for Standardization, 1997.
ISO/IEC 10646
ISO (International Organization for Standardization). ISO/IEC 10646-1993 (E). Information technology -- Universal Multiple-Octet Coded Character Set (UCS) -- Part 1: Architecture and Basic Multilingual Plane. [Geneva]: International Organization for Standardization, 1993 (plus amendments AM 1 through AM 7).
The Unicode Consortium. The Unicode Standard, Version 2.0. Reading, Mass.: Addison-Wesley Developers Press, 1996.

A.2 Other References

Aho, Alfred V., Ravi Sethi, and Jeffrey D. Ullman. Compilers: Principles, Techniques, and Tools. Reading: Addison-Wesley, 1986, rpt. corr. 1988.
Berners-Lee et al.
Berners-Lee, T., R. Fielding, and L. Masinter. Uniform Resource Identifiers (URI): Generic Syntax and Semantics. 1997. (Work in progress; see updates to RFC1738.)
Brüggemann-Klein, Anne. Regular Expressions into Finite Automata. Extended abstract in I. Simon, Hrsg., LATIN 1992, S. 97-98. Springer-Verlag, Berlin 1992. Full Version in Theoretical Computer Science 120: 197-213, 1993.
Brüggemann-Klein and Wood
Brüggemann-Klein, Anne, and Derick Wood. Deterministic Regular Languages. Universität Freiburg, Institut für Informatik, Bericht 38, Oktober 1991.
James Clark. Comparison of SGML and XML. See http://www.w3.org/TR/NOTE-sgml-xml-971215.
Lokale Kopie.
IETF (Internet Engineering Task Force). RFC 1738: Uniform Resource Locators (URL), ed. T. Berners-Lee, L. Masinter, M. McCahill. 1994.
IETF (Internet Engineering Task Force). RFC 1808: Relative Uniform Resource Locators, ed. R. Fielding. 1995.
IETF (Internet Engineering Task Force). RFC 2141: URN Syntax, ed. R. Moats. 1997.
ISO 8879
ISO (International Organization for Standardization). ISO 8879:1986(E). Information processing -- Text and Office Systems -- Standard Generalized Markup Language (SGML). First edition -- 1986-10-15. [Geneva]: International Organization for Standardization, 1986.
ISO/IEC 10744
ISO (International Organization for Standardization). ISO/IEC 10744-1992 (E). Information technology -- Hypermedia/Time-based Structuring Language (HyTime). [Geneva]: International Organization for Standardization, 1992. Extended Facilities Annexe. [Geneva]: International Organization for Standardization, 1996.

B. Character Classes

Following the characteristics defined in the Unicode standard, characters are classed as base characters (among others, these contain the alphabetic characters of the Latin alphabet, without diacritics), ideographic characters, and combining characters (among others, this class contains most diacritics); these classes combine to form the class of letters. Digits and extenders are also distinguished.


[84] LetterBaseCharIdeographic

Letter enthält die scripts der basic multilingual plane. BaseChar enthält die scripts von den ersten 51 (hex33) Zeilen bis hin zu den Hangul Syllables mit Ausnahme der CJK Unified Ideographs, die in Ideographic sind und mit Ausnahme derer aus den productions 86 bis 89.

[85]BaseChar [#x0041-#x005A] | [#x0061-#x007A] | [#x00C0-#x00D6] | [#x00D8-#x00F6] | [#x00F8-#x00FF] | [#x0100-#x0131] | [#x0134-#x013E] | [#x0141-#x0148] | [#x014A-#x017E] | [#x0180-#x01C3] | [#x01CD-#x01F0] | [#x01F4-#x01F5] | [#x01FA-#x0217] | [#x0250-#x02A8] | [#x02BB-#x02C1] | #x0386 | [#x0388-#x038A] | #x038C | [#x038E-#x03A1] | [#x03A3-#x03CE] | [#x03D0-#x03D6] | #x03DA | #x03DC | #x03DE | #x03E0 | [#x03E2-#x03F3] | [#x0401-#x040C] | [#x040E-#x044F] | [#x0451-#x045C] | [#x045E-#x0481] | [#x0490-#x04C4] | [#x04C7-#x04C8] | [#x04CB-#x04CC] | [#x04D0-#x04EB] | [#x04EE-#x04F5] | [#x04F8-#x04F9] | [#x0531-#x0556] | #x0559 | [#x0561-#x0586] | [#x05D0-#x05EA] | [#x05F0-#x05F2] | [#x0621-#x063A] | [#x0641-#x064A] | [#x0671-#x06B7] | [#x06BA-#x06BE] | [#x06C0-#x06CE] | [#x06D0-#x06D3] | #x06D5 | [#x06E5-#x06E6] | [#x0905-#x0939] | #x093D | [#x0958-#x0961] | [#x0985-#x098C] | [#x098F-#x0990] | [#x0993-#x09A8] | [#x09AA-#x09B0] | #x09B2 | [#x09B6-#x09B9] | [#x09DC-#x09DD] | [#x09DF-#x09E1] | [#x09F0-#x09F1] | [#x0A05-#x0A0A] | [#x0A0F-#x0A10] | [#x0A13-#x0A28] | [#x0A2A-#x0A30] | [#x0A32-#x0A33] | [#x0A35-#x0A36] | [#x0A38-#x0A39] | [#x0A59-#x0A5C] | #x0A5E | [#x0A72-#x0A74] | [#x0A85-#x0A8B] | #x0A8D | [#x0A8F-#x0A91] | [#x0A93-#x0AA8] | [#x0AAA-#x0AB0] | [#x0AB2-#x0AB3] | [#x0AB5-#x0AB9] | #x0ABD | #x0AE0 | [#x0B05-#x0B0C] | [#x0B0F-#x0B10] | [#x0B13-#x0B28] | [#x0B2A-#x0B30] | [#x0B32-#x0B33] | [#x0B36-#x0B39] | #x0B3D | [#x0B5C-#x0B5D] | [#x0B5F-#x0B61] | [#x0B85-#x0B8A] | [#x0B8E-#x0B90] | [#x0B92-#x0B95] | [#x0B99-#x0B9A] | #x0B9C | [#x0B9E-#x0B9F] | [#x0BA3-#x0BA4] | [#x0BA8-#x0BAA] | [#x0BAE-#x0BB5] | [#x0BB7-#x0BB9] | [#x0C05-#x0C0C] | [#x0C0E-#x0C10] | [#x0C12-#x0C28] | [#x0C2A-#x0C33] | [#x0C35-#x0C39] | [#x0C60-#x0C61] | [#x0C85-#x0C8C] | [#x0C8E-#x0C90] | [#x0C92-#x0CA8] | [#x0CAA-#x0CB3] | [#x0CB5-#x0CB9] | #x0CDE | [#x0CE0-#x0CE1] | [#x0D05-#x0D0C] | [#x0D0E-#x0D10] | [#x0D12-#x0D28] | [#x0D2A-#x0D39] | [#x0D60-#x0D61] | [#x0E01-#x0E2E] | #x0E30 | [#x0E32-#x0E33] | [#x0E40-#x0E45] | [#x0E81-#x0E82] | #x0E84 | [#x0E87-#x0E88] | #x0E8A | #x0E8D | [#x0E94-#x0E97] | [#x0E99-#x0E9F] | [#x0EA1-#x0EA3] | #x0EA5 | #x0EA7 | [#x0EAA-#x0EAB] | [#x0EAD-#x0EAE] | #x0EB0 | [#x0EB2-#x0EB3] | #x0EBD | [#x0EC0-#x0EC4] | [#x0F40-#x0F47] | [#x0F49-#x0F69] | [#x10A0-#x10C5] | [#x10D0-#x10F6] | #x1100 | [#x1102-#x1103] | [#x1105-#x1107] | #x1109 | [#x110B-#x110C] | [#x110E-#x1112] | #x113C | #x113E | #x1140 | #x114C | #x114E | #x1150 | [#x1154-#x1155] | #x1159 | [#x115F-#x1161] | #x1163 | #x1165 | #x1167 | #x1169 | [#x116D-#x116E] | [#x1172-#x1173] | #x1175 | #x119E | #x11A8 | #x11AB | [#x11AE-#x11AF] | [#x11B7-#x11B8] | #x11BA | [#x11BC-#x11C2] | #x11EB | #x11F0 | #x11F9 | [#x1E00-#x1E9B] | [#x1EA0-#x1EF9] | [#x1F00-#x1F15] | [#x1F18-#x1F1D] | [#x1F20-#x1F45] | [#x1F48-#x1F4D] | [#x1F50-#x1F57] | #x1F59 | #x1F5B | #x1F5D | [#x1F5F-#x1F7D] | [#x1F80-#x1FB4] | [#x1FB6-#x1FBC] | #x1FBE | [#x1FC2-#x1FC4] | [#x1FC6-#x1FCC] | [#x1FD0-#x1FD3] | [#x1FD6-#x1FDB] | [#x1FE0-#x1FEC] | [#x1FF2-#x1FF4] | [#x1FF6-#x1FFC] | #x2126 | [#x212A-#x212B] | #x212E | [#x2180-#x2182] | [#x3041-#x3094] | [#x30A1-#x30FA] | [#x3105-#x312C] | [#xAC00-#xD7A3]

Ideographic enthält die CJK Unified Ideographs der basic multilingual plane.

[86]Ideographic [#x4E00-#x9FA5] | #x3007 | [#x3021-#x3029] [87]CombiningChar [#x0300-#x0345] | [#x0360-#x0361] | [#x0483-#x0486] | [#x0591-#x05A1] | [#x05A3-#x05B9] | [#x05BB-#x05BD] | #x05BF | [#x05C1-#x05C2] | #x05C4 | [#x064B-#x0652] | #x0670 | [#x06D6-#x06DC] | [#x06DD-#x06DF] | [#x06E0-#x06E4] | [#x06E7-#x06E8] | [#x06EA-#x06ED] | [#x0901-#x0903] | #x093C | [#x093E-#x094C] | #x094D | [#x0951-#x0954] | [#x0962-#x0963] | [#x0981-#x0983] | #x09BC | #x09BE | #x09BF | [#x09C0-#x09C4] | [#x09C7-#x09C8] | [#x09CB-#x09CD] | #x09D7 | [#x09E2-#x09E3] | #x0A02 | #x0A3C | #x0A3E | #x0A3F | [#x0A40-#x0A42] | [#x0A47-#x0A48] | [#x0A4B-#x0A4D] | [#x0A70-#x0A71] | [#x0A81-#x0A83] | #x0ABC | [#x0ABE-#x0AC5] | [#x0AC7-#x0AC9] | [#x0ACB-#x0ACD] | [#x0B01-#x0B03] | #x0B3C | [#x0B3E-#x0B43] | [#x0B47-#x0B48] | [#x0B4B-#x0B4D] | [#x0B56-#x0B57] | [#x0B82-#x0B83] | [#x0BBE-#x0BC2] | [#x0BC6-#x0BC8] | [#x0BCA-#x0BCD] | #x0BD7 | [#x0C01-#x0C03] | [#x0C3E-#x0C44] | [#x0C46-#x0C48] | [#x0C4A-#x0C4D] | [#x0C55-#x0C56] | [#x0C82-#x0C83] | [#x0CBE-#x0CC4] | [#x0CC6-#x0CC8] | [#x0CCA-#x0CCD] | [#x0CD5-#x0CD6] | [#x0D02-#x0D03] | [#x0D3E-#x0D43] | [#x0D46-#x0D48] | [#x0D4A-#x0D4D] | #x0D57 | #x0E31 | [#x0E34-#x0E3A] | [#x0E47-#x0E4E] | #x0EB1 | [#x0EB4-#x0EB9] | [#x0EBB-#x0EBC] | [#x0EC8-#x0ECD] | [#x0F18-#x0F19] | #x0F35 | #x0F37 | #x0F39 | #x0F3E | #x0F3F | [#x0F71-#x0F84] | [#x0F86-#x0F8B] | [#x0F90-#x0F95] | #x0F97 | [#x0F99-#x0FAD] | [#x0FB1-#x0FB7] | #x0FB9 | [#x20D0-#x20DC] | #x20E1 | [#x302A-#x302F] | #x3099 | #x309A

Digit enthält die arabischen Ziffern, die Ziffern der indischen Schriften und die Ziffern weiter asiatischer Schriften aus der basic multilingual plane.

[88] Digit[#x0030-#x0039] | [#x0660-#x0669] | [#x06F0-#x06F9] | [#x0966-#x096F] | [#x09E6-#x09EF] | [#x0A66-#x0A6F] | [#x0AE6-#x0AEF] | [#x0B66-#x0B6F] | [#x0BE7-#x0BEF] | [#x0C66-#x0C6F] | [#x0CE6-#x0CEF] | [#x0D66-#x0D6F] | [#x0E50-#x0E59] | [#x0ED0-#x0ED9] | [#x0F20-#x0F29] [89]Extender #x00B7 | #x02D0 | #x02D1 | #x0387 | #x0640 | #x0E46 | #x0EC6 | #x3005 | [#x3031-#x3035] | [#x309D-#x309E] | [#x30FC-#x30FE]

Die Elemente der XML character classes sind einzelne Zeichen des Unicode/ISO 10646 Zeichensatzes.

Die classes der SGML character sind in zwei Gruppen geteilt, eine für die productions (abstract syntax) und eine für die SGML declaration (concrete syntax). Konkrete Zeichen werden in den classes der productions zugewiesen (bis auf das entity end signal). Die classes der SGML declatation haben meist keine oder nur implizite Zuweisungen von konkreten Zeichen wie die beiden wichtigsten Klassen DELMCHAR und DATACHAR. Diese Zeichen können (in SGML) nicht vorgeschrieben werden, weil die delimiter dieselben Zeichen benutzen, die auch in den data vorkommen können. Vielmehr muss sie der Parser auseinanderhalten. Für die Zuweisung der delimiter zu bestimmten Zeichen ist die SGML declaration zuständig. Bei den character classes der SGML declaration können sicher einige wegfallen, aber die Knausrigkeit, mit der die character der abstact syntax vergeben werden, hat ihren guten Sinn.

Mit der Zuweisung von einer begrenzten Anzahl von Zeichen ist die Internationalität der SGML productions und seiner DTDs gewährleistet, weil jedes System der Welt über die ersten 128 Zeichen des Unicode/ISO 10646 Zeichensatzes verfügt. Die "Liberalisierung" der name character sowohl in XML als auch im späteren SGML ist gleichbedeutend mit Provinzialisierung. Hier hat sich das Geteilte, neidisch auf die Erfolge des kleinen Bruders, in das Getrennte verirrt und Schiffbruch erlitten.

The character classes defined here can be derived from the Unicode character database as follows:

Wie SGML mit Unicode/ISO 10646 umgehen wird, ist offen. Vielleicht können isoall, uniall und hanziall einige Anregungen geben.

C. XML and SGML (Non-Normative)

XML is designed to be a subset of SGML, in that every valid XML document should also be a conformant SGML document. For a detailed comparison of the additional restrictions that XML places on documents beyond those of SGML, see [Clark].

Dass XML mit seinem Schwarm von Nachfolgestandards, die das bei SGML Eingesparte nachträglich wieder an XML angehängt haben, SGML nicht Paroli bieten konnte, ist hinreichend bekannt. Gleichzeitig hat XML auf dem Gebiet des Getrennten Vieles erreicht, was in SGML nicht möglich ist. Daher wäre vielleicht der nächste Schritt, die XML productions DTD-tauglich zu machen. Und vielleicht ergibt sich daraus als letzter Schritt, XML zu einem tatsächlichen subset von SGML zu machen, was es jetzt nicht ist. Davon müssten beide Seiten profitieren.

D. Expansion of Entity and Character References (Non-Normative)

This appendix contains some examples illustrating the sequence of entity- and character-reference recognition and expansion, as specified in "4.4 XML Processor Treatment of Entities and References".

If the DTD contains the declaration

<!ENTITY example "<p>An ampersand (&#38;#38;) may be escaped

numerically (&#38;#38;#38;) or with a general entity

(&amp;amp;).</p>" >

then the XML processor will recognize the character references when it parses the entity declaration, and resolve them before storing the following string as the value of the entity "example":

<p>An ampersand (&#38;) may be escaped

numerically (&#38;#38;) or with a general entity


A reference in the document to "&example;" will cause the text to be reparsed, at which time the start- and end-tags of the "p" element will be recognized and the three references will be recognized and expanded, resulting in a "p" element with the following content (all data, no delimiters or markup):

An ampersand (&) may be escaped

numerically (&#38;) or with a general entity


A more complex example will illustrate the rules and their effects fully. In the following example, the line numbers are solely for reference.

1 <?xml version=’1.0’?>

2 <!DOCTYPE test [

3 <!ELEMENT test (#PCDATA) >

4 <!ENTITY % xx ’&#37;zz;’>

5 <!ENTITY % zz ’&#60;!ENTITY tricky "error-prone" >’ >

6 %xx;

7 ]>

8 <test>This sample shows a &tricky; method.</test>

This produces the following:

In der Dokumentation von html4 gibt es ein Beispiel der Verwendung von general entities in SGML.

E. Deterministic Content Models (Non-Normative)

For compatibility, it is required that content models in element type declarations be deterministic.

SGML requires deterministic content models (it calls them "unambiguous"); XML processors built using SGML systems may flag non-deterministic content models as errors.

For example, the content model ((b, c) | (b, d)) is non-deterministic, because given an initial b the parser cannot know which b in the model is being matched without looking ahead to see which element follows the b. In this case, the two references to b can be collapsed into a single reference, making the model read (b, (c | d)). An initial b now clearly matches only a single name in the content model. The parser doesn’t need to look ahead to see what follows; either c or d would be accepted.

More formally: a finite state automaton may be constructed from the content model using the standard algorithms, e.g. algorithm 3.5 in section 3.9 of Aho, Sethi, and Ullman [Aho/Ullman]. In many such algorithms, a follow set is constructed for each position in the regular expression (i.e., each leaf node in the syntax tree for the regular expression); if any position has a follow set in which more than one following position is labeled with the same element type name, then the content model is in error and may be reported as an error.

Algorithms exist which allow many but not all non-deterministic content models to be reduced automatically to equivalent deterministic models; see Brüggemann-Klein 1991 [Brüggemann-Klein].

F. Autodetection of Character Encodings (Non-Normative)

The XML encoding declaration functions as an internal label on each entity, indicating which character encoding is in use. Before an XML processor can read the internal label, however, it apparently has to know what character encoding is in use--which is what the internal label is trying to indicate. In the general case, this is a hopeless situation. It is not entirely hopeless in XML, however, because XML limits the general case in two ways: each implementation is assumed to support only a finite set of character encodings, and the XML encoding declaration is restricted in position and content in order to make it feasible to autodetect the character encoding in use in each entity in normal cases. Also, in many cases other sources of information are available in addition to the XML data stream itself. Two cases may be distinguished, depending on whether the XML entity is presented to the processor without, or with, any accompanying (external) information. We consider the first case first.

Because each XML entity not in UTF-8 or UTF-16 format must begin with an XML encoding declaration, in which the first characters must be ’<?xml’, any conforming processor can detect, after two to four octets of input, which of the following cases apply. In reading this list, it may help to know that in UCS-4, ’<’ is "#x0000003C" and ’?’ is "#x0000003F", and the Byte Order Mark required of UTF-16 data streams is "#xFEFF".

This level of autodetection is enough to read the XML encoding declaration and parse the character-encoding identifier, which is still necessary to distinguish the individual members of each family of encodings (e.g. to tell UTF-8 from 8859, and the parts of 8859 from each other, or to distinguish the specific EBCDIC code page in use, and so on).

Because the contents of the encoding declaration are restricted to ASCII characters, a processor can reliably read the entire encoding declaration as soon as it has detected which family of encodings is in use. Since in practice, all widely used character encodings fall into one of the categories above, the XML encoding declaration allows reasonably reliable in-band labeling of character encodings, even when external sources of information at the operating-system or transport-protocol level are unreliable.

Once the processor has detected the character encoding in use, it can act appropriately, whether by invoking a separate input routine for each case, or by calling the proper conversion function on each character of input.

Like any self-labeling system, the XML encoding declaration will not work if any software changes the entity’s character set or encoding without updating the encoding declaration. Implementors of character-encoding routines should be careful to ensure the accuracy of the internal and external information used to label the entity.

The second possible case occurs when the XML entity is accompanied by encoding information, as in some file systems and some network protocols. When multiple sources of information are available, their relative priority and the preferred method of handling conflict should be specified as part of the higher-level protocol used to deliver XML. Rules for the relative priority of the internal label and the MIME-type label in an external header, for example, should be part of the RFC document defining the text/xml and application/xml MIME types. In the interests of interoperability, however, the following rules are recommended.

These rules apply only in the absence of protocol-level documentation; in particular, when the MIME types text/xml and application/xml are defined, the recommendations of the relevant RFC will supersede these rules.

G. W3C XML Working Group (Non-Normative)

This specification was prepared and approved for publication by the W3C XML Working Group (WG). WG approval of this specification does not necessarily imply that all WG members voted for its approval. The current and former members of the XML WG are:

Jon Bosak, Sun (Chair); James Clark (Technical Lead); Tim Bray, Textuality and Netscape (XML Co-editor); Jean Paoli, Microsoft (XML Co-editor); C. M. Sperberg-McQueen, U. of Ill. (XML Co-editor); Dan Connolly, W3C (W3C Liaison); Paula Angerstein, Texcel; Steve DeRose, INSO; Dave Hollander, HP; Eliot Kimber, ISOGEN; Eve Maler, ArborText; Tom Magliery, NCSA; Murray Maloney, Muzmo and Grif; Makoto Murata, Fuji Xerox Information Systems; Joel Nava, Adobe; Conleth O’Connell, Vignette; Peter Sharpe, SoftQuad; John Tigue, DataChannel

Copyright  ©  1998 W3C (MIT, INRIA, ), All Rights Reserved. W3C liability, trademark, document use and software licensing rules apply.