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Document Description Languages

TITLE: Recent Changes to ISO 8879
(C) Copyright 1998 International Organization for Standardization
PROJECT: JTC1.18.15.1
PROJECT EDITOR: Charles F. Goldfarb
STATUS: Personal Contribution on behalf of editing group.
ACTION: For approval by WG4
SUMMARY OF MAJOR POINTS: This document collects in one place the changes made to ISO 8879 in 1997 (which are the only changes made since 1988). It incorporates corrections to Annexes K and L that are still undergoing formal approval.
DATE: 26 February 1998
DISTRIBUTION: WG4 members and liaisons
REPLYTO: Dr. James D. Mason
(ISO/IEC JTC1/WG4 Convenor)
Information Management Services
1060 Commerce Park
Oak Ridge, TN 37830 U.S.A.
Telephone: +1 423 574-6973
Facsimile: +1 423 574-6983
Network: masonjd@ornl.gov

Recent Changes to ISO 8879

All occurrences of "element declaration" in this International Standard are changed to "element type declaration".

All occurrences of "element set" in this International Standard are changed to "element type set".

Replace 4.223 with:

4.223 owner identifier: The portion of a public identifier that identifies its owner.

Note: The owner of a public identifier is not necessarily the owner of the object that it identifies.

Add the following normative annexes J and K, and informative annex L, to ISO 8879.

Annex J (normative)
Extended Naming Rules

This annex describes an optional extension of SGML known as the "Extended Naming Rules". The extension should be used only in SGML documents for which the normal naming rules are unsuitable (usually because of the size of the natural language character set). An SGML system need not support these Extended Naming Rules in order to be a conforming SGML system.

This annex is phrased in terms of revisions to be made to the body of this International Standard. However, these revisions are applicable only when the Extended Naming Rules are in use.

To distinguish SGML declarations that use this extension from those that do not, the minimum literal in productions [171] and [200] of ISO 8879:1986 must be modified to read "ISO 8879:1986 (ENR)". To accomplish this add the following sentence to the paragraph immediately following production [171] and to the second paragraph following production [200]:

However, when extended naming rules are used, the minimum data must be "ISO 8879:1986 (ENR)".

The extended naming rules are as follows.

For many languages the distinction made in production [189] between uppercase and lowercase is not relevant. It is, therefore, necessary to modify clause 13.4.5 to allow for both an extended character set and for the use of character sets that do not have different cases. The changes required, in the order of their occurrence in 13.4.5, are:

  1. Replace production [189] with:
    [189] naming rules =
     "NAMING", ps+,
     "LCNMSTRT", (ps+, extended naming value)+, ps+,
     "UCNMSTRT", (ps+, extended naming value)+, ps+,
     ("NAMESTRT", (ps+, extended naming value)+, ps+)?,
     "LCNMCHAR", (ps+, extended naming value)+, ps+,
     "UCNMCHAR", (ps+, extended naming value)+, ps+,
     ("NAMECHAR", (ps+, extended naming value)+, ps+)?,
     "NAMECASE", ps+,
     "GENERAL", ps+, ("NO"| "YES"), ps+,
     "ENTITY", ps+, ("NO"| "YES") 
  2. In the "where" list change each occurrence of the phrase "in the literals (if any)" to "identified by the extended naming value (if any)"
  3. Add two new keywords to the "where" list:
    means that each character identified by the extended naming value (if any) is assigned both to LCNMSTRT and as the associated upper-case form in UCNMSTRT.
    means that each character identified by the extended naming value (if any) is assigned both to LCNMCHAR and as the associated upper-case form in UCNMCHAR.
  4. At the end of the clause, add:

    [189.1] extended naming value = parameter literal | character number | character range

    A character number may be used to specify a character that is defined in the syntax-reference character set but is not permitted in an SGML declaration.

    [189.2] character range = character number, ps*, minus, ps*, character number

    Specifying a character range is equivalent to specifying every character number from (and including) the character number that starts the range to (and including) the character number that ends the range.

Annex K (normative)
Web SGML Adaptations

This annex remedies defects revealed by the multiple adaptations of SGML for the World Wide Web (WWW), intranets, and extranets. The annex corrects errors, resolves ambiguities for which there is a clear resolution that does not cause existing conforming documents to become non-conforming, and provides a choice of alternative resolutions for other ambiguities. Although motivated by the World Wide Web, applicability of this annex extends to all uses of SGML.

This annex makes reference to groves and property sets, which are defined in the SGML Extended Facilities of the 2nd Edition of HyTime (ISO/IEC 10744) and also in DSSSL (ISO/IEC 10179).

K.1 Conformance

The decision to conform to this annex is made for individual documents and is indicated in the SGML declaration, as described below (K.3.2). An SGML system need not support this annex in order to be a conforming SGML system.

This annex is organized as a set of replacement and new syntax productions, and is phrased in terms of modifications to be made to the body of this International Standard. However, these modifications are applicable only when conforming to this annex.

An SGML parser that supports this annex shall be able to parse conforming SGML documents that do not claim conformance to it. The parsing of such documents must produce the same grove as would a conforming SGML parser that does not support this annex. Error reporting for such documents, however, is with respect to the standard as modified by this annex; errors with respect to the unmodified standard need not be reported.

K.2 Definitions

K.2.1 Definitions related to document type declarations

K.2.1.1 DTD declarations:

Markup declarations that occur in the external and internal subsets of document type declarations.

K.2.1.2 external subset:

The portion of a document type declaration subset referenced by the external identifier parameter of a document type declaration.

K.2.1.3 internal subset:

The portion of a document type declaration subset that occurs between the dso and dsc of a document type declaration.

If the dso and dsc are omitted, the internal subset is empty (rather than non-existent).

K.2.2 Definitions related to validity assertions

K.2.2.1 fully-tagged document instance:

A document instance in which a start-tag with a generic identifier, and an end-tag, are present for every element, and the attribute name is present in every attribute specification in the start-tag.

Note 1: An SGML declaration requires document instances to be fully-tagged if it specifies OMITTAG NO and SHORTTAG STARTTAG EMPTY NO and ATTRIB OMITNAME NO. A system should offer means, such as a parameter to the invocation of processing, to request validation of whether an instance is fully-tagged even when the SGML declaration does not require it to be.

K.2.2.2 fully-declared document instance:

A document instance for which all markup declarations required for it by the body of this International Standard are explicitly present in its associated document type declaration.

The document type declaration itself could be an implied declaration, as provided in clause K.4.9.

Note 2: An SGML declaration requires document instances to be fully-declared if it specifies IMPLYDEF ATTLIST NO and ELEMENT NO ENTITY NO NOTATION NO. A system should offer means, such as a parameter to the invocation of processing, to request validation of whether an instance is fully-declared even when the SGML declaration does not require it to be.

K.2.2.3 type-valid document instance:

A document instance that conforms to such markup declarations as are required for it by the body of this International Standard that are present in its associated document type declaration.

K.2.3 Definitions related to entity constraints

Note 3: An SGML system that supports unconstrained SGML documents must be able to parse DTD declarations and resolve both internal and external entity references. If it continues parsing (as a form of error-recovery) after failing to access a referenced entity, the results are unpredictable. Observing one or more of the entity constraints defined in this International Standard may cause a document to be more amenable to processing by a simpler SGML system, or in an environment (such as a network) where access to external entities may be slow or unreliable.

K.2.3.1 integrally-stored document instance:

A document instance in which every element and marked section ends in the entity in which it begins.

Note 4: This constraint makes it possible, as a form of error-recovery, for parsing to continue in a fully-tagged document instance after a failure to access a referenced entity. The resulting grove will be the same for the parsed text, except for the tree addresses of younger siblings of the nodes in the inaccessible entity. The constraint also has implementation benefits for editors, "lazy" replacement of entity references, and sharing of grove portions when entities are reused.

K.2.3.2 reference-free document:

An SGML document that has no entity references other than references to predefined data character entities.

Note 5: A reference-free document can be parsed by conforming SGML systems that cannot resolve entity references.

K.2.3.3 external-reference-free document:

An SGML document that has no external entity references.

Note 6: An external-reference-free document could have attribute values that contain names of external entities or that otherwise might cause an application to access an external entity by means other than entity references.

Note 7: External-reference-free documents can be parsed by systems that cannot resolve external entity-references.

K.2.4 Other definitions

K.2.4.1 predefined data character entity:

A general entity, associated with a character number in the syntax-reference character set, that is used to reference significant SGML characters as data.

Note 8: In order to allow delimiter escaping when parsing without respect to DTD declarations, there should be a predefined data character entity for the first character of each delimiter string that can be recognized in a mode where data can occur.

K.2.4.2 white space:

The characters assigned to the SEPCHAR, SPACE, RE, and RS functions.

K.3 SGML declaration

[171] SGML declaration =

"<!SGML", ps+,

(SGML declaration body | SGML declaration reference),

ps*, ">"

In order for SGML documents to be self-identifying, it is strongly recommended that all conforming SGML documents contain one of the forms of SGML declaration.

K.3.1 SGML declaration reference

[171.2] SGML declaration reference =

name, external identifier?


"name" is a name in the reference concrete syntax.

"external identifier" must reference an SGML declaration body. If

  omitted, the external identifier is "SYSTEM".

A public identifier, if formal, shall use the public text class ( "SD" to identify an SGML declaration body.

Note 9: For example:

<!SGML HTML3.2 PUBLIC "+//IDN W3C.ORG//SD HTML Version 3.2//EN">

K.3.2 Version literal

[171.1] SGML declaration body = ps*,

minimum literal, ps+,

document character set, ps+,

capacity set, ps+,

concrete syntax scope, ps+,

concrete syntax, ps+,

feature use, ps+,

application-specific information,

(ps+, added requirements)?

The minimum data of the minimum literal shall be one of the following:

The ENR suffix indicates that the document conforms to Annex J of this International Standard.

The WWW suffix indicates that the document conforms to Annex K (this annex) of this International Standard, which incorporates by reference the provisions of Annex J of this International Standard and supersedes any contradictory provisions elsewhere in this International Standard.

Note 10: Certain parameters of the SGML declaration body are omissible in order to allow existing documents to conform to this annex by a simple change to the minimum data. Nevertheless, it is recommended that all parameters be specified.

K.3.3 Capacity Set

[180] capacity set =

"CAPACITY", ps+,

(("PUBLIC", ps+, public identifier)|


("SGMLREF", (ps+, name, ps+, number)*))

NONE indicates that no capacities are specified.

Specifying NONE does not require a system to support capacities greater than those specified in its system declaration.

K.3.4 Concrete syntax

[182] concrete syntax =

"SYNTAX", ps+,

(public concrete syntax |

(shunned character number identification, ps+,

syntax-reference character set, ps+,

function character identification, ps+,

naming rules, ps+,

delimiter set, ps+,

reserved name use, ps+,

quantity set,

(ps+, predefined data character entities)?))

K.3.4.1 Quantity Set

[194] quantity set =

"QUANTITY", ps+,


("SGMLREF", (ps+, name, ps+, number)*))

NONE indicates that no quantities are specified.

Specifying NONE does not require a system to support quantities greater than those specified in its system declaration.

K.3.4.2 Predefined data character entities

[194.1] predefined data character entities =

"ENTITIES", ps+,

("NONE"|(parameter literal, ps+, character number)+)

Each interpreted "parameter literal" must be a valid general entity name in the syntax being defined, and is associated with a character number in the syntax-reference character set. When the named entity is referenced, the replacement text is a numeric character reference to the corresponding character. Predefined data character entities are treated as though defined at the start of the internal subset of all documents in which the concrete syntax is used.

Note 11: For example:

ENTITIES "amp" 38 "lt" 60 "gt" 62 "quot" 34 "apos" 39

K.3.5 Markup minimization features

[196] markup minimization features =

"MINIMIZE", ps+,

"DATATAG", ps+, ("NO"|"YES"), ps+,

"OMITTAG", ps+, ("NO"|"YES"), ps+,

"RANK", ps+, ("NO"|"YES"), ps+,

"SHORTTAG", ps+, ("NO"|"YES"|

(start-tag options, ps+, end-tag options, ps+, attribute-options)),

(ps+, empty element ending rules,

ps+, implied default declarations)?

K.3.5.1 SHORTTAG start-tag options

[196.1] start-tag options =

"STARTTAG", ps+,

"EMPTY", ps+, ("NO"|"YES"), ps+,

"UNCLOSED", ps+, ("NO"|"YES"), ps+,



EMPTY YES enables empty start-tags.

UNCLOSED YES enables unclosed start-tags.

NETENABL ALL permits NET-enabling start-tags and NULL end-tags; and

IMMEDNET restricts them to elements with empty syntactic content that

  must be ended by a NET, so it cannot be specified if EMPTYNRM NO is


Note 12: An element with empty syntactic content need not have been declared EMPTY.

K.3.5.2 SHORTTAG end-tag options

[196.2] end-tag options =

"ENDTAG", ps+,

"EMPTY", ps+, ("NO"|"YES"), ps+,

"UNCLOSED", ps+, ("NO"|"YES")


EMPTY YES enables empty end-tags.

UNCLOSED YES enables unclosed end-tags.

K.3.5.3 SHORTTAG attribute options

[196.3] attribute options =

"ATTRIB", ps+,

"DEFAULT", ps+, ("NO"|"YES"), ps+,

"OMITNAME", ps+, ("NO"|"YES"), ps+,

"VALUE", ps+, ("NO"|"YES")


DEFAULT YES enables attribute value defaulting (

OMITNAME YES allows attribute names and vi to be omitted for

  unique NMTOKEN values (

VALUE YES allows some attribute values to be specified without

  delimiters, rather than as literals (

Note 13: DEFAULT NO does not bar default values from attribute definition list declarations.

K.3.6 Empty element ending rules

[196.4] empty element ending rules =

"EMPTYNRM", ps+, ("NO"|"YES")


EMPTYNRM YES applies normal rules for the presence of end-tags, including

  markup minimization rules, to elements of a type declared EMPTY, or

  that are forced to be EMPTY by an explicit content reference

  attribute (7.3.).

Note 14: Specifying EMPTYNRM YES applies to mandatorily empty elements the same rules about the presence of end-tags that apply to other kinds of elements.

K.3.7 Implied default declarations

[196.5] implied default declarations =

"IMPLYDEF", ps+,

"ATTLIST", ps+, ("NO"|"YES"), ps+,

"DOCTYPE", ps+, ("NO"|"YES"), ps+,

"ELEMENT", ps+, ("NO"|"YES"), ps+,

"ENTITY", ps+, ("NO"|"YES"), ps+,

"NOTATION", ps+, ("NO"|"YES")


DOCTYPE YES means that an implied document type declaration includes

  an implied declaration for an external subset entity (see K.4.9); and

YES for the other parameters allows information of the specified type

  to be used in the document instance without an explicit declaration.

  A declaration is implied, as follows:

ATTLIST YES means an undeclared attribute is declared as: CDATA #IMPLIED

ELEMENT YES means an undeclared element type is declared as: - - ANY

ENTITY YES means an undeclared general entity is declared as: SYSTEM

NOTATION YES means an undeclared notation is declared as: SYSTEM

Note 15: IMPLYDEF DOCTYPE YES implies only a declaration for an external subset entity. Other declarations may be implied if needed, and if permitted by the applicable IMPLYDEF parameters.

When IMPLYDEF ENTITY is specified, #DEFAULT cannot be specified as a general entity name.

Implicitly declared definitions occur in the grove in the order in which it is necessary to imply their declarations. No attribute assignment node is created for an attribute unless the attribute is specified.

Note 16: An implied declaration is not necessarily the same as an explicit declaration for the same object that was ignored during parsing (Note 29). Nor does it constrain any explicit declaration that might be created for that object as a result of processing (for example, when generating an explicit DTD for a document that has none).

K.3.8 Other features

[198] other features =

"OTHER", ps+,

"CONCUR", ps+, ("NO"|("YES", ps+, number)), ps+,

"SUBDOC", ps+, ("NO"|("YES", ps+, number)), ps+,

"FORMAL", ps+, ("NO"|"YES"),

(urn feature, keeprsre feature, validity feature, entities feature)?

K.3.8.1 Universal Resource Names

[198.1] urn feature =

ps+, "URN", ps+, ("NO"|"YES")


URN YES means public identifiers are interpreted according to the

  applicable Internet Engineering Task Force RFC2141 governing

  Universal Resource Names.

If both URN and FORMAL are YES, public identifiers are interpreted either as formal public identifiers or as URNs.

K.3.8.2 White space in content

[198.2] keeprsre feature =

ps+, "KEEPRSRE", ps+, ("YES"|"NO")


KEEPRSRE YES means clause 7.6.1 does not apply.

Note 17: If KEEPRSRE YES is specified, all white space in mixed content is included in the grove as datachar nodes.

Note 18: This option does not affect delimited strings, such as attribute value literals, which have their own rules for normalizing white space (and which, in any case, do not occur in content).

K.3.8.3 Assertions

[198.3] validity feature = ps+,



NOASSERT makes no validity assertion.

TYPE asserts that document instances are type-valid.

If the parameter is omitted, TYPE is assumed.

[198.4] entities feature = ps+,


                 ("REF", ps+, ("NONE"|"INTERNAL"|"ANY"), ps+,

                 "INTEGRAL", ps+, ("NO"|"YES")))


NOASSERT makes no validity assertion.

REF asserts the document either has unconstrained entity references (ANY),

    is external-reference-free (INTERNAL), or is reference-free (NONE).

INTEGRAL YES asserts document instances are integrally-stored.

If the parameter is omitted, NOASSERT is assumed.

It is a reportable markup error if a document is less constrained than is asserted.

Note 19: For example, if an otherwise conforming document incorrectly asserts that it is integrally-stored, the document is non-conforming. Had the assertion not been made, the document would have been conforming.

Note 20: A system should offer means, such as a parameter to the invocation of processing, to check whether a particular VALIDITY or ENTITIES assertion could correctly be made for a document, even when the SGML declaration does not make that assertion.

Note 21: To satisfy the classical requirement for SGML conformance, a document instance must be fully-declared as well as type-valid.

K.3.9 Added requirements

[199.1] added requirements =

"SEEALSO", ps+, ("NONE"| (ps+, public identifier)+)

The public identifiers identify additional requirements for the document, including requirements unrelated to the SGML language. These requirements are in addition to, and must not contradict, the requirements of this International Standard. Failure to satisfy the added requirements is not a reportable markup error, except to the extent that such requirements are also expressed in other parameters of the SGML declaration.

Note 22: For example, this parameter could be used by an SGML system to signal the existence of requirements for specific entity constraint assertions, formatting conventions for specified element types, or data restrictions, such as that the number of cells in a table row does not exceed the number specified in some attribute. It is not a reportable markup error if the added required entity assertions are not present in the SGML declaration; if they are present, it is a reportable markup error if the the document fails to satisfy them, as that would have been the case even in the absence of the added requirements.

It is not an error if the system is unable to access an object named by the public identifiers.

Note 23: See Annex L "Added Requirements for XML" for an example.

K.4 General

K.4.1 Hexadecimal character reference

[62] character reference =

named character reference |

numeric character reference |

hex character reference

[62.1] named character reference =

cro, function name, reference end

[62.2] numeric character reference =

cro, character number, reference end

[62.3] hex character reference =

hcro, hexdigit+, reference end

A hexdigit is a digit or lowercase a-f or uppercase A-F. The length of the hex digit string cannot exceed NAMELEN.

K.4.2 Delimiters (9.6)

Name  String  Number     Mode        Constraint  Description

HCRO  (none)  (none)     CON LIT     HEX         Hex character reference open

NESTC (NET)   (none)     TAG                     NET-enabling start-tag close

NET   /       47         CON         ELEM        Null end-tag

HEX constraint: must be followed by a hexdigit.

If no assignment is made to NESTC, the NET is used.

K.4.3 NET-enabling start-tag

[18] net-enabling start-tag =


generic identifier specification, attribute specification list, s*,


K.4.4 Attribute definitions

[141] attribute definition list declaration =

mdo, "ATTLIST", ps+,

((associated element type | (rni, ("IMPLICIT"|"ALL")))|

(rni, "NOTATION", ps+,

(associated notation name | (rni, ("IMPLICIT"|"ALL"))))), ps+,

attribute definition list,

ps*, mdc

where the keywords indicate the objects associated with the attributes:

NOTATION indicates that the associated objects are notations.

IMPLICIT means all the implicitly defined element types or notations.

ALL means all element types or notations.

[149.1] associated notation name =

(notation name | name group)

IMPLICIT and ALL are the equivalent of name groups.

The same element type or notation may be the associated object in multiple ATTLIST declarations. An attempt to redefine an attribute that was previously defined for an associated object is not an error; the earliest definition prevails (just as for entity declarations). However, definitions associated with ALL can be overridden by subsequent attribute declarations for specific element types or notations, including definitions specified with IMPLICIT.

K.4.4.1 Possibly empty attribute definition list

[142] attribute definition list =

attribute definition?, (ps+, attribute definition)*

K.4.4.2 Data specification

[145] declared value =



notation|name token group|data specification

[145.1] data specification =

"DATA", ps+, notation name, data attribute specification?


"notation name" identifies the data content notation of the

  attribute's value

"data attribute specification" specifies the corresponding data


The value of an attribute whose declared value is "data specification" is character data.

Note 24: An application may wish to verify that the value of a data specification attribute is meaningful in light of the specified notation name and data attributes, but it is not an SGML error if this is not the case.

K.4.5 Implied document type name

[111] document type name =

(generic identifier | (rni, "IMPLIED"))


IMPLIED means the document element can have any valid element type


It is a reportable markup error if IMPLIED is specified and the start-tag of the document element is omitted or does not contain a generic identifier.

IMPLIED cannot be specified if LINK EXPLICIT YES or CONCUR YES are specified in the SGML declaration.

K.4.6 Internet domain names in public identifiers

[80] owner identifier =

ISO owner identifier |

registered owner identifier |

unregistered owner identifier |

internet domain name owner identifier

[83.1] internet domain name owner identifier =

"+//IDN ", minimum data

where the minimum data must begin with an internet domain name.

Note 25: The string "IDN domain.name" is treated as an ISO/IEC 9070 "registered owner prefix". Any sub-domain names could be expressed as owner name components. For example, the internet domain name in "http://www.someisp.net/users/mtb" could occur in an FPI as:

+//IDN someisp.net::www::users::mtb

or as:

+//IDN www.someisp.net/users/mtb

Note 26: When constructing a public text owner identifier using an internet domain name, users may wish to consider the name's potential lifespan and that of the objects to be identified by public identifiers that use it.

Semicolon, exclamation point, asterisk, number sign, commercial at sign, dollar sign, underscore, and percent sign are members of the abstract character class "special", which is usable in minimum data.

K.4.7 Elements

An element of a type declared EMPTY, or that is forced to be EMPTY by an explicit content reference attribute, cannot contain any text, including white space, other markup, or included subelements. Markup minimization can be applied to such elements (7.3).

K.4.8 Entities

K.4.8.1 Token separators (10.1.3)

A referenced parameter entity must consist of zero or more of the consecutive complete tokens that follow the ts in which the reference occurs in the same group (i.e., at the same nesting level), together with any intervening ts separators and connectors, and optionally with surrounding separators and connectors. The entity must end within the same group.

An Ee can occur in a ts only if the reference to the entity the Ee terminates occurs in the same group (i.e., at the same nesting level).

K.4.8.2 Entity set

[113] entity set =

(entity declaration |

attribute definition list declaration |

notation declaration |



The keyword "NOTATION" must be specified in the attribute

definition list declaration.

K.4.8.3 SGML subdocument entity

[3] SGML subdocument entity =

(s*, SGML declaration)?, prolog, document instance set, Ee

If the SGML declaration is omitted, the subdocument uses the SGML declaration applicable to the entity from which the subdocument entity is referenced.

K.4.9 Omitted prolog (7.1)

If LINK EXPLICIT NO and CONCUR NO are specified in the SGML declaration and either or both of IMPLYDEF DOCTYPE YES or IMPLYDEF ELEMENT YES are specified, the SGML document entity need not contain a prolog. In such cases, a prolog will be implied consisting solely of a single implied document type declaration, as follows:

Note 27: When both the document type name and the external subset entity are implied in a document type declaration, a system may be able to locate an appropriate external subset by considering the storage identifier of the SGML document entity and/or the generic identifier of the document element.

If permitted by the implied default declarations parameter of the SGML declaration, a document type declaration (whether explicit or implied) may lack declarations for element types, attributes, notations, and/or general entities. Declarations are implied for them as provided in K.3.7.

Note 28: Care should be taken to insure that markup minimization in the instance does not obscure the element structure and cause the parser to misunderstand the intended implied declarations.

Note 29: If some or all of an instance's associated document type declaration should be unavailable or for other reasons ignored during parsing, it is recommended that the constructed grove be the same as if implied declarations had replaced the ignored ones.

Annex L (informative): Added Requirements for XML

This annex illustrates the relationship of SGML declarations to "added requirements" by means of a real-world example, XML. It is not intended as a specification for XML.

L.1 Application summary

The Extensible Markup Language (XML) is the core subset of SGML functionality developed by the World Wide Web Consortium (W3C) for exchanging SGML documents over the World Wide Web. The current specification for XML can be found at the W3C web site at "http://www.w3.org/TR/" under the title "Extensible Markup Language (XML).

The XML specification covers the following aspects of an SGML application and system:

  1. Restrictions on the use of some SGML language constructs.
  2. A required character set and mandatory encodings.
  3. Rules for the behavior of the entity manager.
  4. Application semantics of the type appropriate for an enabling architecture; that is, less than a complete DTD and associated semantics. In contrast, SGML applications, such as HTML, would normally have a complete DTD with semantics defined for all element types and attributes.
  5. Details of the interface between applications and an SGML/XML parser beyond what is addressed in ISO 8879 and related standards.

XML distinguishes two classes of conforming documents:

A full-SGML validating parser cannot validate documents for conformance to XML unless it is specially modified to support XML. That is because some of XML's language restrictions cannot be expressed in the SGML declaration. Those restrictions can be found in http://www.w3.org/TR/NOTE-sgml-xml.

L.2 SGML Declaration for XML

XML documents implicitly contain an SGML declaration, which differs slightly depending on whether the document is "valid". XML documents that are well-formed but not valid implicitly contain the following SGML declaration.

<!SGML -- SGML Declaration for XML --

     "ISO 8879:1986 (WWW)"



    "ISO Registration Number 176//CHARSET

    ISO/IEC 10646-1:1993 UCS-4 with implementation

    level 3//ESC 2/5 2/15 4/6"


    0       9       UNUSED

    9       2       9

    11      2       UNUSED

    13      1       13

    14      18      UNUSED

    32      95      32

    127     1       UNUSED

    128     32      UNUSED

    160     55136   160

    55296   2048    UNUSED  -- surrogates --

    57344   8190    57344

    65534   2       UNUSED  -- FFFE and FFFF --

    65536   1048576 65536





  BASESET "ISO Registration Number 176//CHARSET

          ISO/IEC 10646-1:1993 UCS-4 with implementation

          level 3//ESC 2/5 2/15 4/6"


    0 1114112 0


    RE    13

    RS    10

    SPACE 32






      58 95 192-214 216-246 248-305 308-318 321-328

      330-382 384-451 461-496 500-501 506-535 592-680

      699-705 902 904-906 908 910-929 931-974 976-982

      986 988 990 992 994-1011 1025-1036 1038-1103

      1105-1116 1118-1153 1168-1220 1223-1224

      1227-1228 1232-1259 1262-1269 1272-1273

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