This section is normative.
In order to ensure that XHTML modules are maximally portable, this specification rigidly defines conformance requirements. 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.
This specification defines a method for defining XHTML-conforming modules. A module conforms to this specification when it meets all of the following criteria:
Names for XHTML-conforming 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 modules are defined through XML
Formal Public Identifiers (FPIs). Within FPIs, fields are
separated by double slash character sequences
//). The various fields MUST be composed as
-". For formal standards, this field MUST be the formal reference to the standard (e.g.
ELEMENTS XHTML-followed by an organization-defined unique identifier (e.g. MyML 1.0). This identifier is SHOULD be composed of a unique name and a version identifier that can be updated as the document type evolves.
Using these rules, the name for an XHTML conforming module
Naming Rules are critical for portability of user agents and XHTML-conforming tools. These rules need to be simple enough that they can be readily adhered to, and need to convey upon document type and module designers the power to readily associate their creations with XHTML (for marketing purposes, if nothing else). The above rules address these concerns. There were some other possibilities for naming conventions, and they were not used for the following reasons:
In the case of new modules, there is no need to associate the module with a specific version of XHTML - the name does not need to identify version dependencies.