The W3C specification for the Modularization of XHTML has passed CR review and has been promoted to a W3C Proposed Recommendation. The Proposed Recommendation "specifies an abstract modularization of XHTML and an implementation of the abstraction using XML Document Type Definitions (DTDs). This modularization provides a means for subsetting and extending XHTML, a feature needed for extending XHTML's reach onto emerging platforms... XHTML is the reformulation of HTML 4 as an application of XML. XHTML 1.0 specifies three XML document types that correspond to the three HTML 4 DTDs: Strict, Transitional, and Frameset. XHTML 'Modularization' is a decomposition of XHTML 1.0, and by reference HTML 4, into a collection of abstract modules that provide specific types of functionality; these abstract modules are implemented in the specification using the XML Document Type Definition language, but an implementation using XML Schemas is expected."
Modularization of XHTML. Reference: W3C Proposed Recommendation 22-February-2001. Edited by Murray Altheim (Sun Microsystems), Frank Boumphrey (HTML Writers Guild), Sam Dooley (IBM), Shane McCarron (Applied Testing and Technology), Sebastian Schnitzenbaumer (Mozquito Technologies), and Ted Wugofski (Openwave -formerly Gateway). This PR supersedes the previous CR version of 2000-10-20; a color-keyed diff-marked version reveals changes vis-à-vis the Candidate Recommendation version. The PR review period extends until 22-March-2001, after which time the specification may become a W3C Recommendation. The PR is also available as a single HTML document, in Postscript, in PDF, and in a .ZIP archive.
The normative Annex D ('Building DTD Modules') describes how "XHTML modules are implemented as DTD fragments. When these fragments are assembled in a specific manner, the resulting DTD is a representation of a complete document type. This representation can then be used for validation of instances of the document type. The key to combining these fragments into a meaningful DTD is the rules used to define the fragments. This section defines those rules. When these rules are followed, DTD authors can be confident that their modules will interface cleanly with other XHTML-compatible modules. Modules conforming to these rules also need to satisfy the conformance requirements defined in XHTML Family Module Conformance in order to be called XHTML Family Modules.."
"The modularization of XHTML refers to the task of specifying well-defined sets of XHTML elements that can be combined and extended by document authors, document type architects, other XML standards specifications, and application and product designers to make it economically feasible for content developers to deliver content on a greater number and diversity of platforms.
"Over the last couple of years, many specialized markets have begun looking to HTML as a content language. There is a great movement toward using HTML across increasingly diverse computing platforms. Currently there is activity to move HTML onto mobile devices (hand held computers, portable phones, etc.), television devices (digital televisions, TV-based web browsers, etc.), and appliances (fixed function devices). Each of these devices has different requirements and constraints.
"Modularizing XHTML provides a means for product designers to specify which elements are supported by a device using standard building blocks and standard methods for specifying which building blocks are used. These modules serve as "points of conformance" for the content community. The content community can now target the installed base that supports a certain collection of modules, rather than worry about the installed base that supports this permutation of XHTML elements or that permutation of XHTML elements. The use of standards is critical for modularized XHTML to be successful on a large scale. It is not economically feasible for content developers to tailor content to each and every permutation of XHTML elements. By specifying a standard, either software processes can autonomously tailor content to a device, or the device can automatically load the software required to process a module.
"Modularization also allows for the extension of XHTML's layout and presentation capabilities, using the extensibility of XML, without breaking the XHTML standard. This development path provides a stable, useful, and implementable framework for content developers and publishers to manage the rapid pace of technological change on the Web.