3. Conformance Definition

Contents

This section is normative.

In order to ensure that XHTML-family documents are maximally portable among XHTML-family user agents, this specification rigidly defines conformance requirements for both of these and for XHTML-family document types. While the conformance definitions can be found in this section, they necessarily reference normative text within this document, within the base XHTML specification [XHTML1], and within other related specifications. It is only possible to fully comprehend the conformance requirements of XHTML through a complete reading of all normative references.

3.1. XHTML Host Language Document Type Conformance

It is possible to modify existing document types and define wholly new document types using both modules defined in this specification and other modules. Such a document type is "XHTML Host Language Conforming" when it meets the following criteria:

  1. The document type must be defined using one of the implementation methods defined by the W3C (currently this is limited to XML DTDs, but XML Schema will be available soon).
  2. The document type must have a unique identifier as defined in Naming Rules that uses the string "XHTML" in its first token of the public text description.
  3. The document type must include, at a minimum, the Structure, Hypertext, Basic Text, and List modules defined in this specification.
  4. For each of the W3C-defined modules that are included, all of the elements, attributes, types of attributes (including any required enumerated value lists), and any required minimal content models must be included (and optionally extended) in the document type's content model. When content models are extended, all of the elements and attributes (along with their types or any required enumerated value lists) required in the original content model must continue to be required.
  5. The document type may define additional elements and attributes. However, these must be in their own XML Namespace [XMLNAMES].

3.2. XHTML Integration Set Document Type Conformance

It is also possible to define document types that are based upon XHTML, but do not adhere to its structure. Such a document type is "XHTML Integration Set Conforming" when it meets the following criteria:

  1. The document type must be defined using one of the implementation methods defined by the W3C (currently this is limited to XML DTDs, but XML Schema will be available soon).
  2. The document type must have a unique identifier as defined in Naming Rules that uses the string "XHTML" NOT in its first token of the public text description.
  3. The document type must include, at a minimum, the Hypertext, Basic Text, and List modules defined in this specification.
  4. For each of the W3C-defined modules that are included, all of the elements, attributes, types of attributes (including any required enumerated lists), and any required minimal content models must be included (and optionally extended) in the document type's content model. When content models are extended, all of the elements and attributes (along with their types or any required enumerated value lists) required in the original content model must continue to be required.
  5. The document type may define additional elements and attributes. However, these must be in their own XML Namespace [XMLNAMES].

3.3. XHTML Family Module Conformance

This specification defines a method for defining XHTML-conforming modules. A module conforms to this specification when it meets all of the following criteria:

  1. The module must be defined using one of the implementation methods identified in this specification (currently only XML DTDs are defined).
  2. The module must have a unique identifier as defined in Naming Rules.
  3. When the module is implemented using an XML DTD, the module must insulate its parameter entity names through the use of unique prefixes or other, similar methods.
  4. The module must have a prose definition that describes the syntactic and semantic requirements of the elements, attributes, and/or content models that it declares.
  5. The module must not reuse any element names that are defined in other W3C-defined modules, except when the content model and semantics of those elements are either identical to the original or an extension of the original, or when the reused element names are within their own namespace (see below).
  6. The module's elements and attributes must be part of an XML Namespace [XMLNAMES]. If the module is defined by an organization other than the W3C, this namespace must NOT be the same as the namespace in which other W3C modules are defined.

3.4. XHTML Family Document Conformance

A conforming XHTML family document is a valid instance of a conforming XHTML Host Language Conforming Document Type.

3.5. XHTML Family User Agent Conformance

A conforming user agent must meet all of the following criteria (as defined in [XHTML1]):

  1. In order to be consistent with the XML 1.0 Recommendation [XML], the user agent must parse and evaluate an XHTML document for well-formedness. If the user agent claims to be a validating user agent, it must also validate documents against their referenced DTDs according to [XML].
  2. When the user agent claims to support facilities defined within this specification or required by this specification through normative reference, it must do so in ways consistent with the facilities' definition.
  3. When a user agent processes an XHTML document as generic XML, it shall only recognize attributes of type ID (e.g., the id attribute on most XHTML elements) as fragment identifiers.
  4. If a user agent encounters an element it does not recognize, it must continue to process the children of that element. If the content is text, the text must be presented to the user.
  5. If a user agent encounters an attribute it does not recognize, it must ignore the entire attribute specification (i.e., the attribute and its value).
  6. If a user agent encounters an attribute value it doesn't recognize, it must use the default attribute value.
  7. If it encounters an entity reference (other than one of the predefined entities) for which the User Agent has processed no declaration (which could happen if the declaration is in the external subset which the User Agent hasn't read), the entity reference should be rendered as the characters (starting with the ampersand and ending with the semi-colon) that make up the entity reference.
  8. When rendering content, User Agents that encounter characters or character entity references that are recognized but not renderable should display the document in such a way that it is obvious to the user that normal rendering has not taken place.
  9. The use agent must process whitespace characters according to the following rules. The following characters are defined in [XML] as whitespace characters:

    The XML processor normalizes different system's line end codes into one single line-feed character, that is passed up to the application. The XHTML user agent in addition, must treat the following characters as whitespace:

    Whitespace is handled according to the following rules:

    Whitespace in attribute values is processed according to [XML].

3.6. Naming Rules

XHTML host language document types must adhere to strict naming conventions so that it is possible for software and users to readily determine the relationship of document types to XHTML. The names for document types implemented as XML Document Type Definitions are defined through Formal Public Identifiers (FPIs). Within FPIs, fields are separated by double slash character sequences (//). The various fields MUST be composed as follows:

  1. The leading field must be "-" to indicate a privately defined resource.
  2. The second field MUST contain the name of the organization responsible for maintaining the named item. There is no formal registry for these organization names. Each organization SHOULD define a name that is unique. The name used by the W3C is, for example, W3C.
  3. The third field MUST begin with the token XHTML if the document type is Host Language conforming. It may contain the string XHTML anywhere but the first token if the document type is Integration Set conforming. No other document types may use the token XHTML in their third field. The field must also contain an organization-defined unique identifier (e.g., MyML 1.0). This identifier SHOULD be composed of a unique name and a version identifier that can be updated as the document type evolves.
  4. The fourth field defines the language in which the item is developed (e.g., EN).

Using these rules, the name for an XHTML Host Language conforming document type might be -//MyCompany//XHTML DTD MyML 1.0//EN. The name for an XHTML family conforming module might be -//MyCompany//XHTML ELEMENTS MyElements 1.0//EN. The name for an XHTML Integration Set conforming document type might be -//MyCompany//Special Markup with XHTML//EN.