This section is normative.
This document defines a variety of XHTML modules and the semantics of those modules. This section describes the conventions used in those module definitions.
An abstract module is a definition of an XHTML module using prose text and some informal markup conventions. While such a definition is not generally useful in the machine processing of document types, it is critical in helping people understand what is contained in a module. This section defines the way in which XHTML abstract modules are defined. An XHTML-conforming module is not required to provide an abstract module definition. However, anyone developing an XHTML module is encouraged to provide an abstraction to ease in the use of that module.
The abstract modules are not defined in a formal grammar. However, the definitions do adhere to the following syntactic conventions. These conventions are similar to those of XML DTDs, and should be familiar to XML DTD authors. Each discrete syntactic element can be combined with others to make more complex expressions that conform to the algebra defined here.
Abstract module definitions define minimal, atomic content models for each module. These minimal content models reference the elements in the module itself. They may also reference elements in other modules upon which the abstract module depends. Finally, the content model in many cases requires that text be permitted as content to one or more elements. In these cases, the symbol used for text is PCDATA (parsed characted data). This is a term, defined in the XML 1.0 Recommendation, that refers to processed character data. A content type can also be defined as EMPTY, meaning the element has no content in its minimal content model.
In some instances, it is necessary to define the types of attribute values or the explicit set of permitted values for attributes. The following attribute types (defined in the XML 1.0 Recommendation) are used in the definitions of the abstract modules:
In addition to these pre-defined data types, XHTML Modularization defines the following data types and their semantics (as appropriate):
Data type Description Character A single character, as per section 2.2 of [XML]. Characters A white space separated list of Character values. Charset A character encoding, as per [RFC2045]. Encodings A comma-separated list of 'charset's with optional q parameters, as defined in section 14.2 of [RFC2616] as the field value of the Accept-Charset request header. ContentType A media type, as per [RFC2045]. ContentTypes Attributes of this type identify the allowable content type(s) of an associated URI (usually a value of another attribute on the same element). At its most general, it is a comma-separated list of media ranges with optional accept parameters, as defined in section 14.1 of [RFC2616] as the field value of the accept request header.In its simplest case, this is just a media type, such as "image/png" or "application/xml", but it may also contain asterisks, such as "image/*" or "*/*", or lists of acceptable media types, such as "image/png, image/gif, image/jpeg".
The user agent must combine this list with its own list of acceptable media types by taking the intersection, and then use the resulting list as the field value of the accept request header when requesting the resource using HTTP.
For instance, if the attribute specifies the value "image/png, image/gif, image/jpeg", but the user agent does not accept images of type "image/gif" then the resultant accept header would contain "image/png, image/jpeg".
A user agent must imitate similar behavior when using other methods than HTTP. For instance, when accessing files in a local filestore, <p src="logo" srctype="image/png, image/jpeg"> might cause the user agent first to look for a file logo.png, and then for logo.jpg.
If a value for the content type is not given, "*/*" must be used for its value.
For the current list of registered content types, please consult [MIMETYPES].
Coordinates Comma separated list of Lengths used in defining areas. CURIE A Compact URI [CURIE]. CURIEs One or more white space separated CURIE values Datetime Date and time information, as defined by the typedateTime in [XMLSCHEMA] except that the timezone part is required. HrefTarget Name used as destination for results of certain actions, with legal values as defined by NMTOKEN. LanguageCode A language code. The values should conform to [RFC3066] or its successors. LanguageCodes A comma-separated list of language ranges with optional q parameters, as defined in section 14.4 of [RFC2616] as the field value of the Accept-Language request header. Individual language codes should conform to [RFC3066] or its successors. Length Either a number, representing a number of pixels, or a percentage, representing a percentage of the available horizontal or vertical space. Thus, the value "50%" means half of the available space. LocationPath A location path as defined in [XPATH]. MediaDesc
A comma-separated list of media descriptors as described by [CSS2]. The default is all.
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