The CALS Table Model is a standard for representing tables in SGML / XML . It was developed as part of the Continuous Acquisition and Life-cycle Support (CALS) initiative by the United States Department of Defense .
90-636: The CALS Table Model was developed by the Continuous Acquisition and Life-cycle Support (CALS) Industry Steering Group Electronic Publishing Committee (EPC). The EPC subcommittee, of which Harvey Bingham was co-chair and a major contributor, designed the CALS Table Model in 1989–1990. The EPC was made up of industry and military service representatives. Some represented traditional military document printing agencies. Others represented electronic publishing organizations. SGML itself
180-512: A data: URI (so as to avoid requiring network access) containing the definitions for the character entities . The sole function of an FPI in HTML 5's HTML (as opposed to XHTML) representation is triggering legacy modes. The WHATWG HTML standard specifies a list of which FPIs should trigger quirks mode. These include the FPIs for various vendor-customised HTML DTDs. They also include the FPIs for
270-400: A XML Catalog ) the schema used in the parsed XML document and that is validated in another language. A common misconception holds that a non-validating XML parser does not have to read document type declarations, when in fact, the document type declarations must still be scanned for correct syntax as well as validity of declarations, and the parser must still parse all entity declarations in
360-465: A coded character set , NOTATION to a format such as a file format (either for references to entities from external files, or for interpreting a textual format contained within an element), and NONSGML to an asset in a non-SGML format. The space after the text class name is followed by the sequence -// if the FPI refers to unavailable public text —i.e. a document, file or specification which
450-416: A document type for an SGML -family markup language ( GML , SGML , XML , HTML ). The DTD specification file can be used to validate documents. A DTD defines the valid building blocks of an XML document. It defines the document structure with a list of validated elements and attributes. A DTD can be declared inline inside an XML document, or as an external reference. A namespace-aware version of DTDs
540-821: A document type definition (DTD). The particular DTD version in use was specified in a document type declaration using an FPI, sometimes (especially in the later versions, and required in XML as mentioned above) in combination with a URL for the DTD file as a system identifier. In contrast to the SGML declaration for XML, the SGML declaration for HTML enabled the FORMAL feature, meaning that public identifiers used for and within HTML DTDs were required to be FPIs. A document type declaration (for HTML 4.01 Strict) containing an FPI: The FPI in
630-516: A macro . The entity declaration assigns it a value that is retained throughout the document. A common use is to have a name more recognizable than a numeric character reference for an unfamiliar character. Entities help to improve legibility of an XML text. In general, there are two types: internal and external. An example of internal entity declarations (here in an internal DTD subset of an SGML document) is: Internal entities may be defined in any order, as long as they are not referenced and parsed in
720-537: A storage object identifier ), the SGML FORMAL feature is disabled in XML, since the format of public identifiers is not specified by XML (i.e. they are not explicitly required to be FPIs, although they may be). The only details which the XML specification stipulates about the public identifier are that it may be given alongside the system identifier, and may be used by an XML processor along with other information to determine an alternative URI (failing which, it
810-424: A MIME type, interpreted as a relative URI, but it could be an absolute URI to a specific renderer, or a URN indicating an OS-specific object identifier such as a UUID). The declared notation name must be unique within all the document type declaration, i.e. in the external subset as well as the internal subset, at least for conformance with XML. Notations can be associated to unparsed external entities included in
900-408: A better way to validate XML structure. A DTD is associated with an XML or SGML document by means of a document type declaration (DOCTYPE). The DOCTYPE appears in the syntactic fragment doctypedecl near the start of an XML document. The declaration establishes that the document is an instance of the type defined by the referenced DTD. DOCTYPEs make two sorts of declarations: The declarations in
990-408: A fixed value ( #FIXED ), or which value should be used as a default value ("…") in case the given attribute is left out in an XML tag. Attribute list declarations are ignored by non-validating SGML and XML parsers (in which cases any attribute is accepted within all elements of the parsed document), but these declarations are still checked for well-formedness and validity. An entity is similar to
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#17327808280691080-492: A later extension added to the standard as an annex, which also specifies certain extensions required by XML. LPD refers to an SGML link process definition (defining a transformation from one SGML format to another). ELEMENTS , ENTITIES and SHORTREF refer to portions of a document type definition (DTD) consisting of specific types of markup declaration. DTD refers to an entire DTD. The remaining three refer to concepts from outside of SGML: CHARSET refers to
1170-408: A notation name "type-image-svg". However, notation names usually follow a naming convention that is specific to the application generating or using the notation: notations are interpreted as additional meta-data whose effective content is an external entity and either a PUBLIC FPI, registered in the catalogs used by XML or SGML parsers, or a SYSTEM URI, whose interpretation is application dependent (here
1260-446: A notation named "type-image-svg" that references the standard public FPI and the system identifier (the standard URI) of an SVG 1.1 document, instead of specifying just a system identifier as in the first example (which was a relative URI interpreted locally as a MIME type). This annotation is referenced directly within the unparsed "type" attribute of the "img" element, but its content is not retrieved. It also declares another notation for
1350-506: A profile of SGML, except in its XHTML representation. As such, it is not defined using a DTD. Early drafts for HTML 5 used the NONSGML -type FPI -//WHATWG//NONSGML HTML5//EN in the DOCTYPE in place of a DTD FPI, since it did not activate Internet Explorer 6's quirks mode. This was ultimately done away with altogether, and the final HTML 5 DOCTYPE does not use an FPI. The preferred form
1440-467: A resolvable location. SGML allows mapping public identifiers to system identifiers in catalogs that are optionally available to the URI resolvers used by document parsing software. This DOCTYPE can only appear after the optional XML declaration , and before the document body, if the document syntax conforms to XML. This includes XHTML documents: An additional internal subset can also be provided after
1530-455: A resource from versions in other languages or language varieties. In accordance with recommendations made by ISO 9070 , Steven DeRose and David G. Durand suggest using XX if no ISO 639 code is applicable. The specification notes that while the language of the resource might affect the data and names defined and the language of any source-code comments, the language affects the usability of some text classes more than others. For example,
1620-716: A single slash ( / ) for that purpose); the year follows any part number if present, and is separated by a colon ( : ). An unregistered owner identifier begins with -// . Owners which use unregistered identifiers include the W3C ( -//W3C ), the Internet Engineering Task Force ( -//IETF ), the United States Department of Defense ( -//USA-DOD ), the European Parliament ( -//EP ) and others. Since it
1710-464: A single space. There are three types of owner identifier, distinguished by their first three characters, which are ISO for an ISO owner identifier , -// for an unregistered owner identifier or +// for a registered owner identifier . An ISO owner identifier is either an ISO publication number such as ISO 8879:1986 , or an ISO-IR registration number given as e.g. ISO Registration Number 111 for ISO-IR-111 . The latter type
1800-505: A subdocument entity (with the SUBDOC keyword in the entity declaration, i.e. interpreted with their own individual schemas, namespaces, and so forth). Those of the DOCUMENT class are not intended to be referenced as an entity from an enclosing document. CAPACITY and SYNTAX refer to portions of an SGML declaration. SD (for an entire SGML declaration) was added to this list by
1890-406: A vendor-specific application, to annotate the "sgml" root element in the document. In both cases, the declared notation named is used directly in a declared "type" attribute, whose content is specified in the DTD with the "NOTATION" attribute type (this "type" attribute is declared for the "sgml" element, as well as for the "img" element). However, the "title" attribute of the "img" element specifies
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#17327808280691980-433: A way that it becomes possible to parse XML documents with non-validating XML parsers (if the only purpose of the external DTD subset was to define the schema). In addition, documents for these XML schema languages must be parsed separately, so validating the schema of XML documents in pure standalone mode is not really possible with these languages: the document type declaration remains necessary for at least identifying (with
2070-417: Is actually registered is the registered owner prefix , which follows the +// and may optionally be followed by one or more owner-assigned portions which might identify, for example, departments within an organisation. If owner name components additional to the registered prefix are used, they are separated from the prefix by a :: pair. A registered owner prefix conforming to ISO 9070 may be one of
2160-446: Is also declared with its own notation). Notations are also completely opaque for XML and SGML parsers, so they are not differentiated by the type of the external entity that they may reference (for these parsers they just have a unique name associated to a public identifier (an FPI) and/or a system identifier (a URI)). Some applications (but not XML or SGML parsers themselves) also allow referencing notations indirectly by naming them in
2250-528: Is being developed as Part 9 of ISO DSDL . DTDs persist in applications that need special publishing characters, such as the XML and HTML Character Entity References , which derive from larger sets defined as part of the ISO SGML standard effort. XML uses a subset of SGML DTD. As of 2009 , newer XML namespace -aware schema languages (such as W3C XML Schema and ISO RELAX NG ) have largely superseded DTDs as
2340-405: Is less common for XML formats to use a DTD (such as which might use FPIs for notations or external entities), and thus less common for one to contain a DOCTYPE referencing a DTD (either by FPI or only by URI—although a DOCTYPE may still be used for entity definitions embedded within the XML file itself). For example, most versions of RSS (excepting RSS 0.91) do not have an official DTD. Similarly,
2430-497: Is located by its defined SYSTEM identifier "example1.svg" (also interpreted as a relative URI). The effective content for the "img" element be the content of this second external resource. The difference with the GIF image, is that the SVG image is parsed within the SGML document, according to the declarations in the DTD, where the GIF image is just referenced as an opaque external object (which
2520-410: Is not accessible). However, such documents are still fully parsable in the non -standalone mode of validating parsers, which signals an error if it can not locate these external entities with their specified public identifier (FPI) or system identifier (a URI), or are inaccessible. (Notations declared in the DTD are also referencing external entities, but these unparsed entities are not needed for
2610-448: Is not available for access or purchase by the general public. The public text description follows this marker; for an available public text , the description immediately follows the space after the text class name. For an ISO publication, the description is taken from the final element of the title of the publication, not counting any part number; otherwise, it can be any suitably unique string of permitted characters. The description
2700-488: Is not parsable with SGML) via its "data" attribute (whose value type is an opaque ENTITY). Only one notation name may be specified in the value of ENTITY attributes (there is no support in SGML, XML 1.0 or XML 1.1 for multiple notation names in the same declared external ENTITY, so separate attributes are needed). However multiple external entities may be referenced (in a space-separated list of names) in attributes declared with type ENTITIES, and where each named external entity
2790-466: Is not registered, it is not guaranteed to be unique (another owner may choose the same owner identifier), which weakens the uniqueness guarantee of the FPI as a whole, although it is still guaranteed to be distinct both from all other FPIs with the same owner, and also from all FPIs with registered owners. A registered owner identifier begins with the characters +// . It refers to a registered identifier as stipulated by ISO 9070 . The portion which
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2880-438: Is only permitted for CHARSET FPIs (see below). In either case, it is distinguished by beginning with the characters ISO , and does not require any prefix before those characters. The year was formerly separated from the standard number by a hyphen ( - , e.g. ISO 8879-1986 ), which use is now deprecated . The hyphen is now, instead, used to separate the part number from the standard number (replacing earlier use of
2970-424: Is parsed as if it was: Reference to the "author" internal entity is not substituted in the replacement text of the "signature" internal entity. Instead, it is replaced only when the "signature" entity reference is parsed within the content of the "sgml" element, but only by validating parsers (non-validating parsers do not substitute entity references occurring within contents of element or within attribute values, in
3060-427: Is required to use the URI given in the system identifier). Identifying strings for XML namespaces are required to be non-empty URIs (such as an absolute URL; use of relative URLs is deprecated), although they are not required to be resolvable URLs and may, for example, be URNs . Additionally, alternative schema formats such as XML Schema (XSD) serve as a competitor to DTD in an XML context, overcoming some of
3150-441: Is simply <!DOCTYPE html> (with neither a public nor system identifier), although a system identifier of about:legacy-compat (using the about: URI scheme ) is condoned. The XML representation (XHTML), by contrast, is permitted but not required to bear any DOCTYPE, but no validating DTD is provided for the HTML 5 schema. However, various FPIs for XHTML 1.0, XHTML 1.1 and MathML DTDs are defined as instead pointing to
3240-403: Is specified between "&" and ";") are not replaced like usual named entities (defined with a CDATA value), but are left as distinct unparsed tokens that may be used either as the value of an element attribute (like above) or within the element contents, provided that either the DTD allows such external entities in the declared content type of elements or in the declared type of attributes (here
3330-501: Is terminated by another // pair. The part of the FPI following the description depends on the text class. For CHARSET FPIs, it is a public text designating sequence , giving a textual representation of an ISO/IEC 2022 designation escape sequence in column/line notation (e.g. ESC 2/8 4/0 ); registered designation escapes are expected to match the ISO owner identifier given, while private-use designation escapes are namespaced by
3420-434: The "URN:''name''" value of a standard CDATA attribute, everywhere a URI can be specified. However this behaviour is application-specific, and requires that the application maintains a catalog of known URNs to resolve them into the notations that have been parsed in a standard SGML or XML parser. This use allows notations to be defined only in a DTD stored as an external entity and referenced only as
3510-488: The ENTITY type for the data attribute), or the SGML parser is not validating the content. Notations may also be associated directly to elements as additional meta-data, without associating them to another external entity, by giving their names as possible values of some additional attributes (also declared in the DTD within the <!ATTLIST ...> declaration of the element). For example: The example above shows
3600-502: The FORMAL feature name. System identifiers, by contrast, have no structure defined by SGML itself—they might be filenames, database keys or even addresses for indexable storage—but are interpreted by the SGML system's entity manager component to identify the location of the entity. As such, ISO/IEC 8879 itself does not use the term formal system identifier (FSI), which is instead defined in an amendment to ISO/IEC 10744 ( HyTime ). An SGML external identifier consists either of
3690-486: The PUBLIC keyword must, in the syntax for general external identifiers, be followed by literals for both the public and system identifiers. As an exception to this, however, notation declarations may use a public identifier without a system identifier. In contrast to the requirement that the system identifier be a URI (classified for purposes of HyTime as a type of formal system identifier or FSI, or more narrowly as
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3780-555: The DocBook format, which initially used a document type declaration identifying a DTD by an FPI, switched its primary schema definition from DTD to RELAX NG in version 5.0, and ceased to use document type declarations at that time, and Scalable Vector Graphics (SVG) did the same in version 1.2. If a system identifier (such as a path or URL) is not given for a resource identified by a public identifier such as an FPI, an SGML system's entity manager will generate one with reference to
3870-717: The internal subset , and substitute the replacement texts of internal entities occurring anywhere in the document type declaration or in the document body. Formal Public Identifier A Formal Public Identifier ( FPI ) is a short piece of text with a particular structure that may be used to uniquely identify a product, specification or document. FPIs were introduced as part of Standard Generalized Markup Language (SGML), and serve particular purposes in formats historically derived from SGML ( HTML and XML ). Some of their most common uses are as part of document type declarations (DOCTYPEs) and document type definitions (DTDs) in SGML, XML and historically HTML, but they are also used in
3960-655: The type of each attribute value, if not an explicit set of valid values. DTD markup declarations declare which element types , attribute lists , entities , and notations are allowed in the structure of the corresponding class of XML documents. An element type declaration defines an element and its possible content. A valid XML document contains only elements that are defined in the DTD. Various keywords and characters specify an element's content: For example: Element type declarations are ignored by non-validating SGML and XML parsers (in which cases, any elements are accepted in any order, and in any number of occurrences in
4050-413: The vCard and iCalendar file formats to identify the software product which generated the file. More recently, Uniform Resource Identifiers (URIs) and universally unique identifiers (UUIDs) are usually used to uniquely identify objects. FPIs have become a legacy system . An FPI consists of an owner identifier , followed by a double slash ( // ), followed by a text identifier . For example,
4140-471: The "standards mode" of Internet Explorer at the time it was introduced. For example, a DOCTYPE using the HTML 4.01 Strict FPI ( -//W3C//DTD HTML 4.01//EN ) would trigger standards mode in Internet Explorer 6, meaning that it would use a content-box box model, while a DOCTYPE using the HTML 4.01 Transitional FPI ( -//W3C//DTD HTML 4.01 Transitional//EN ) would trigger quirks mode, including
4230-463: The DTD do not need to be in English). The class is separated from the description using a space character; the description is separated from the language using a double slash. The text identifier may optionally contain a version indicator after the language, also separated by a double slash. The text identifier immediately follows the // pair after the owner identifier, and must begin with one of
4320-400: The DTD loses its special role outside the DTD and it becomes a literal character. However, the references to predefined character entities are substituted wherever they occur, without needing a validating parser (they are only introduced by the "&" character). Notations are used in SGML or XML. They provide a complete reference to unparsed external entities whose interpretation is left to
4410-444: The DTD or in the body of the document, in their order of parsing: it is valid to include a reference to a still undefined entity within the content of a parsed entity, but it is invalid to include anywhere else any named entity reference before this entity has been fully defined, including all other internal entities referenced in its defined content (this also prevents circular or recursive definitions of internal entities). This document
4500-745: The DTD or in the document body but not declared: The XML DTD syntax is one of several XML schema languages. However, many of the schema languages do not fully replace the XML DTD. Notably, the XML DTD allows defining entities and notations that have no direct equivalents in DTD-less XML (because internal entities and parsable external entities are not part of XML schema languages, and because other unparsed external entities and notations have no simple equivalent mappings in most XML schema languages). Most XML schema languages are only replacements for element declarations and attribute list declarations, in such
4590-593: The DTDs of the various HTML 2.0 "levels", as well as those for HTML 3.0, 3.2 and the Transitional and Frameset versions of HTML 4.0 and 4.01—except that when the HTML 4.01 (but not HTML 4.0) Transitional and Frameset FPIs are accompanied by a system identifier, they instead trigger almost‑standards mode (renamed to "limited‑quirks mode"). The XHTML 1.0 Transitional and Frameset FPIs trigger limited‑quirks mode unconditionally. Mostly, these are specified as prefixes including
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#17327808280694680-642: The EPC. The differences in interpretation had led to serious interoperability problems. To resolve these differences, OASIS identified a subset of the full CALS table model that had a high probability of successful interoperability among the OASIS vendor products. This subset is the Exchange Table Model DTD. Document type definition A document type definition ( DTD ) is a specification file that contains set of markup declarations that define
4770-649: The FPI owner identifier. As an example of this type of FPI, the FPI ISO Registration Number 177//CHARSET ISO/IEC 10646-1:1993 UCS-4 with implementation level 3//ESC 2/5 2/15 4/6 is used in HTML 4 's SGML declaration to identify Unicode . For all other FPIs (i.e. those where the class is not CHARSET ), the part following the description is a public text language which is a sequence of uppercase letters, strongly encouraged (but not mandated) to be an ISO 639-1 code. Stopping short of mandating
4860-471: The application (which interprets them directly or retrieves the external entity themselves), by assigning them a simple name, which is usable in the body of the document. For example, notations may be used to reference non-XML data in an XML 1.1 document. For example, to annotate SVG images to associate them with a specific renderer: This declares the TEXT of external images with this type, and associates it with
4950-482: The behaviour of the program parsing it, but also upon the ISO-registration status of the organisation responsible for schema referenced by the FPI. SGML uses two forms of identifier for resources: system identifiers are unique and meaningful only within a particular system, while public identifiers are unique and meaningful within a wider scope. The term "public" here does not necessarily mean that
5040-488: The body of the SGML or XML document. The PUBLIC or SYSTEM parameter of these external entities specifies the FPI and/or the URI where the unparsed data of the external entity is located, and the additional NDATA parameter of these defined entities specifies the additional notation (i.e., effectively the MIME type here). For example: Within the body of the SGML document, these referenced external entities (whose name
5130-504: The body of the document. This is possible because the replacement text specified in the internal entity definitions permits a distinction between parameter entity references (that are introduced by the "%" character and whose replacement applies to the parsed DTD contents) and general entity references (that are introduced by the "&" character and whose replacement is delayed until they are effectively parsed and validated). The "%" character for introducing parameter entity references in
5220-570: The browsers in use the time when they were created, which did not necessarily comply with the specifications for, for example, CSS in how they rendered web pages. Since this meant that improving their standards-compliance would cause browsers to display existing web pages incorrectly, browsers used the document type declaration to trigger between "modes" under which the page would be rendered. "Quirks mode" retained legacy behaviour from earlier browser versions to avoid breaking existing pages—for example, Internet Explorer versions 6 and 7 would render
5310-420: The case of unregistered owners with colliding names), while informal public identifiers have no uniqueness guarantee, meaning that those assigned by one owner may collide with formal or informal public identifiers assigned by another. A feature enabling the interpretation of public identifiers using the formal structure, thus requiring public identifiers to be FPIs, can be enabled within the SGML declaration using
5400-470: The changes shifting the focus away from public identifiers such as FPIs and towards standardising the form taken by system identifiers. The system identifier is to be treated as an (absolute or relative) URI , but must not contain a URI fragment identifier (portion beginning with # ). The system identifier is also generally required: the SYSTEM keyword must be followed by a system identifier literal, and
5490-461: The common entity set for HTML 5 and MathML uses the FPI -//W3C//ENTITIES HTML MathML Set//EN//XML . The FPI is undoubtedly the least well-understood part of the document type declaration (DOCTYPE), an integral component of valid HTML , XML and Standard Generalized Markup Language (SGML) documents. The Formal Public Identifier's effect upon its host document is unusual in that it can depend not only upon its own syntactical correctness and
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#17327808280695580-411: The content model of these documents. The following example of a DOCTYPE contains both public and system identifiers: All HTML 4.01 documents conform to one of three SGML DTDs. The public identifiers of these DTDs are constant and are as follows: The system identifiers of these DTDs, if present in the DOCTYPE, are URI references . A system identifier usually points to a specific set of declarations in
5670-618: The designating sequence or language must be the final part, the language code may be followed by another // pair, followed by a public text display version , which specifies a particular platform that the implementation of SGML entities should target. For example, the base ISO 8879:1986//ENTITIES Added Latin 1//EN entity set defines the Latin-1 named entities using tautological SDATA entities, while ISO 8879:1986//ENTITIES Added Latin 1//EN//XML implements them using Unicode code point references for use in XML . Similarly,
5760-676: The document type declaration above reads -//W3C//DTD HTML 4.01//EN , while the URL is given as a system identifier. The FPI was, strictly speaking, optional: it was also possible (but uncommon) to define a custom HTML DTD and omit the FPI; in this case, the inclusion of a system identifier without an FPI is signified by the SYSTEM keyword. One example of such a custom system identifier without an associated FPI is: Since they were principally intended for use by SGML validators, document type declarations were initially ignored by browsers. However, older web pages were designed to display correctly in
5850-411: The external subset of documents, and allows these documents to remain compatible with validating XML or SGML parsers that have no direct support for notations. Notations are not used in HTML, or in basic profiles for XHTML and SVG, because: Even in validating SGML or XML 1.0 or XML 1.1 parsers, the external entities referenced by an FPI and/or URI in declared notations are not retrieved automatically by
5940-406: The external subset: Alternatively, only the internal subset may be provided: Finally, the document type definition may include no subset at all; in that case, it just specifies that the document has a single top-level element (this is an implicit requirement for all valid XML and HTML documents, but not for document fragments or for all SGML documents, whose top-level elements may be different from
6030-464: The following block-capital words followed by a space, specifying the public text class : DOCUMENT , SUBDOC and TEXT refer to SGML documents or fragments of SGML documents. Those of the TEXT class are intended to be referenced using a text entity (without an entity-type keyword, i.e. inserted directly into the document), while those of the SUBDOC class are intended to be referenced using
6120-457: The following: Text identifiers can be broken down into the class , description and language . In the example -//W3C//DTD HTML 4.01//EN , the class is " DTD ", indicating that the FPI represents a document type definition; the description is " HTML 4.01 "; and the language is " EN " which suggests that the document type definition is written in English (though documents conforming to
6210-490: The formal structure, and thus are not FPIs, are sometimes referred to as "informal" public identifiers. Although the constraints of formal (as opposed to informal) public identifiers are an optional feature, due to the specification for FPIs being introduced late in the development of ISO 8879, use of FPIs for public identifiers is strongly recommended, since the FPI structure ensures that the FPIs assigned by one owner do not collide with FPIs assigned by other owners (except in
6300-571: The former name of the Organization for the Advancement of Structured Information Standards ( OASIS ), surveyed the implementing vendors to identify differences as the initial step toward reaching a common interpretation. The next step was an updated CALS Table Model DTD and semantics. Both are now available from OASIS. As implementations of the CALS Table Model were developed, a number of ambiguities and omissions were detected and reported to
6390-469: The identifier " -//W3C//DTD HTML 4.01//EN " can be broken down into two parts: the owner identifier which indicates the issuer of the FPI, and the text identifier which indicates the particular document or object the FPI identifies. In the example, the owner identifier is " -//W3C " and the text identifier is " DTD HTML 4.01//EN ". The text identifier itself consists of multiple constituent parts. Sequences of whitespace are treated as equivalent to
6480-467: The implied root element), and it indicates the type name of the root element: DTDs describe the structure of a class of documents via element and attribute-list declarations. Element declarations name the allowable set of elements within the document, and specify whether and how declared elements and runs of character data may be contained within each element. Attribute-list declarations name the allowable set of attributes for each declared element, including
6570-401: The internal entity "example1SVGTitle" whose declaration that does not define an annotation, so it is parsed by validating parsers and the entity replacement text is "Title of example1.svg". The content of the "img" element references another external entity "example1SVG" whose declaration also does not define an notation, so it is also parsed by validating parsers and the entity replacement text
6660-789: The internal subset form part of the DOCTYPE in the document itself. The declarations in the external subset are located in a separate text file. The external subset may be referenced via a public identifier and/or a system identifier . Programs for reading documents may not be required to read the external subset. Any valid SGML or XML document that references an external subset in its DTD, or whose body contains references to parsed external entities declared in its DTD (including those declared within its internal subset ), may only be partially parsed but cannot be fully validated by validating SGML or XML parsers in their standalone mode (this means that these validating parsers do not attempt to retrieve these external entities, and their replacement text
6750-424: The keyword PUBLIC followed by a literal for the public identifier and an optional literal for the system identifier, or the keyword SYSTEM followed by an optional literal for the system identifier. The literals are prefixed and suffixed with either the literal delimiter or the alternative literal delimiter , usually set by the SGML declaration to the double and single ASCII quotation marks, as they are in
6840-471: The language EN given in the FPI in an HTML 4 or XHTML 1 DOCTYPE declaration should not be changed, regardless of the language of the web page itself; by contrast, the DSSSL stylesheets for DocBook internally use FPIs with different languages to identify string-table entity sets for particular localisations . Additionally, except for CHARSET , CAPACITY , NOTATION and SYNTAX FPIs, for which
6930-428: The limitations of DTDs. XSD can (unlike DTDs) be validated using the same tools as any other XML document, includes support for XML namespaces (which DTDs can only interpret as fixed portions of the element and attribute names in question), allows regular expression constraints to be placed on the format of text data such as telephone numbers, and is better able to express complex content-model structures. Thus, it
7020-490: The local path (relative to the catalog file) to a copy of the Scalable Vector Graphics 1.1 DTD, and specify the SGML declaration (in this case, the declaration for the XML syntax) which an SGML processor should use for it: The schema for the alternative XML catalog format is itself defined in a DTD, itself identified by an FPI ( -//OASIS//DTD Entity Resolution XML Catalog V1.0//EN ). It similarly allow
7110-529: The mappings of FPIs to paths to be expressed although, since it is intended for use only with XML, it does not support specifying an alternative SGML declaration, although extensions exist to express the remainder of the information expressible in an SGML catalog. The above DTD FPI mapping is represented as follows: HTML versions 2 through 4 (including the XML-based XHTML 1.x) were defined as profiles of SGML, and specified with an SGML declaration and
7200-405: The page using the Internet Explorer 5.5 box model. "Standards mode" would conform more closely to the relevant specifications. What was at the time called "almost standards mode" and initially implemented by Firefox and Safari would use traditional behaviour when determining the height of table cells containing images, but otherwise behave like standards mode; this corresponded to the behaviour of
7290-441: The parsed document), but these declarations are still checked for form and validity. An attribute list specifies for a given element type the list of all possible attribute associated with that type. For each possible attribute, it contains: For example: Here are some attribute types supported by both SGML and XML: A default value can define whether an attribute must occur ( #REQUIRED ) or not ( #IMPLIED ), or whether it has
7380-418: The parsers themselves. Instead, these parsers just provide to the application the parsed FPI and/or URI associated to the notations found in the parsed SGML or XML document, and with a facility for a dictionary containing all notation names declared in the DTD; these validating parsers also check the uniqueness of notation name declarations, and report a validation error if some notation names are used anywhere in
7470-429: The public identifier. Although the SGML specification itself does not specify how the entity manager should do this, the intention was for it to use a table mapping public identifiers to system identifiers. Accordingly, an SGML catalog format was created to contain mappings from public to system identifiers; the catalog file can also specify rules for overriding the given system identifier. Although XML mandates
7560-617: The reference concrete syntax for SGML, and also in XML. The use of the SYSTEM keyword in an SGML entity definition without a following system identifier is permitted, if the entity manager is able to resolve the entity from its name alone. External identifiers are used in document type declarations (DOCTYPEs) referencing document type definitions (DTDs), in external entity specifications and notation declarations within DTDs, and in link type declarations referencing link process definitions (LPDs). External identifiers in XML are more constrained than they are in general SGML, with
7650-464: The resource is available to the general public—it may only be available within a single organisation, for example (in which case, it is an unavailable public text )—but only that it exists outside of the context of the particular system environment or document which it is referenced in. An FPI is a "formal" public identifier in the sense that it follows the formal structure laid down by the SGML standard (ISO 8879); public identifiers which do not follow
7740-488: The use of an ISO 639-1 code avoids requiring validating software to check whether the language is an ISO 639-1 code, and also allows for extensibility: for example, a small number of FPIs used in practice use ISO 639-3 codes (such as NDS for Low German ) or IETF language tags with hyphens removed (such as SRLATN for Serbian written in Gajica ) for cases where ISO 639-1 codes prove insufficient for distinguishing
7830-408: The use of an Internet Explorer 5.5 (border-box) box model. In addition to the FPI, browsers would consider the presence or absence of a system identifier when deciding between quirks mode and standards mode. The absence of a DOCTYPE declaration altogether (or, for Internet Explorer 6, the DOCTYPE declaration not being the first line in the file) would trigger quirks mode. HTML 5 is not defined as
7920-570: The use of system identifiers in more places than does SGML itself, catalogs may still be needed for remapping and overriding the given system identifier: a system identifier which is a local path may not be useful on other machines, while one which is a network URL will not be useful when a network connection is not available, for example. Accordingly, an alternative XML-based catalog format exists for use by XML software, supporting rules for replacing or rewriting URIs, as well as for mapping FPIs to URIs. For example, an entry in an SGML catalog may give
8010-409: The validation of documents in the standalone mode of these parsers: the validation of all external entities referenced by notations is left to the application using the SGML or XML parser). Non-validating parsers may eventually attempt to locate these external entities in the non -standalone mode (by partially interpreting the DTD only to resolve their declared parsable entities), but do not validate
8100-556: Was new. At that time, the CALS intent for all their technical manuals was to use that document type definition (DTD) to achieve system-neutral interchange of content and structure. Its basis was a minimal description and example of a table from the prior Mil-M-38784B specification for producing technical manuals. The incomplete specification of the semantics associated with the table model allowed too much freedom for vendor interpretation, and resulted in problems with interchange. SGML-Open,
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