Sustainability of Digital Formats: Planning for Library of Congress Collections

XHTML is an openly documented, freely implementable format for marking up structured documents for use as pages and applications on the World Wide Web. The standard was developed and has been maintained by the World Wide Web Consortium (W3C). The specification for XHTML 1.1 was published as a W3C Recommendation on May 31, 2001, under the auspices of the W3C HTML Working Group. This version of XHTML is based on the Strict profile of XHTML 1.0 (often referred to as XHTML 1.0 Strict) with minor changes. Earlier HTML features that had been deprecated were omitted in XHTML 1.1, in order to "to provide a consistent, forward-looking document type." In general, the working group's strategy was "to define a markup language that is rich in structural functionality, but that relies upon style sheets for presentation." Because XHTML 1.1 is based on XHTML 1.0 Strict, there is no support for laying out pages using frames in a frameset. See Notes below for more on frames and XHTML 1.1.

The other important change from XHTML 1.0 was reformulation into separable modules based on the W3C Recommendation Modularization of XHTML, published on April 10, 2001. This modularization was a decomposition of XHTML 1.0 into a collection of abstract modules that provide specific types of functionality. These modules could be combined with each other and with other modules to create XHTML subset and extension document types that would qualify as members of an XHTML "family" of document types. Rules for defining the abstract modules and for implementing them using XML DTDs were defined. XHTML 1.1 was to serve as the basis for future formats of the XHTML family aimed at particular user agents or application contexts. In 2018, a single extension to XHTML has been identified by the compilers of this resource as reaching the W3C Recommendation status, XHTML+RDFa 1.1. This is a superset of XHTML 1.1 intended for authors who want to create XHTML documents that embed rich semantic markup. In addition to envisioning extensions to XHTML, the working group had developed a specification for XHTML Basic, built on a subset of the modules included in XHTML 1.1. See Notes below for more on XHTML+RDFa and XHTML Basic.

The functional and syntactical differences between the first edition of XHTML 1.1 and the Strict profile of XHTML 1.0 can be summarized as follows:

• On every element, the lang attribute was removed in favor of the xml:lang attribute
• On the a and map elements, the name attribute was removed in favor of the id attribute
• A collection of elements for ruby annotations was added. These are short runs of text alongside the base text, often used in East Asian documents to indicate pronunciation or to provide a short annotation. See W3C Recommendation for Ruby Annotation.

A second edition was published on November 23, 2010. The new edition incorporated clarifications and corrections as a result of several years of use. It also included an XML Schema implementation, and reversed the removal of the lang attribute to increase compatibility with browsers and assistive technologies. XHTML 1.1 is the last XHTML specification to reach the status of a W3C Recommendation. The XML serialization of HTML5 provides a continuing mechanism for delivering content on the web using valid XML.

XHTML is a publicly documented and freely implementable format developed by the World Wide Web Consortium (W3C).

Two editions of XHTML 1.1 were published by as W3C Recommendations:

• XHTML 1.1, Module-based XHTML, published as W3C Recommendation 31 May 2001, by the HTML Working Group.
• XHTML™ 1.1, Module-based XHTML (Second Edition), published as a W3C Recommendation on November 23, 2010 by the XHTML 2 Working Group.

See XHTML_1_0.

Relationship of XHTML 1.1 to earlier HTML document types: In the clause entitled The XHTML 1.1 Document Type, from the specification for XHTML 1.1, the relationship of this format to predecessor formats is described as follows: "The XHTML 1.1 document type is a fully functional document type with rich semantics. It is not, however, as varied in functionality as the XHTML 1.0 Transitional or Frameset document types. These document types defined many presentational components that are better handled through style sheets or other similar mechanisms. Moreover, since the XHTML 1.1 document type is based exclusively upon the facilities defined in the XHTML modules [see Modularization of XHTML], it does not contain any of the deprecated functionality of XHTML 1.0 nor of HTML 4. Despite these exceptions, or perhaps because of them, the XHTML 1.1 document type is a solid basis for future document types that are targeted at varied user agent environments."

Frames in XHTML 1.1: Because XHTML 1.1 is based on XHTML 1.0 Strict, there is no support for the frameset structure, which was introduced in HTML 4.0, and supported in the XHTML 1.0 Frameset profile. The modularization on which XHTML 1.1 is based did identify a Frames Module but this module was not included in the XHTML 1.1 specification.  To use frames in XHTML 1.1, the Frames Module would have needed to be added in to configure an extended document type.  Websites that used frames probably kept using one of the HTML 4.x versions until they constructed an equivalent layout using a style sheet.

XHTML Basic: The specifications for this less powerful version of XHTML [see Format Specifications] begin with the following abstract, "The XHTML Basic document type includes the minimal set of modules required to be an XHTML host language document type, and in addition it includes images, forms, basic tables, and object support. It is designed for Web clients that do not support the full set of XHTML features; for example, Web clients such as mobile phones, PDAs, pagers, and set top boxes. The document type is rich enough for content authoring." The compilers of this resource are not aware of the degree to which XHTML Basic has been used. Comments welcome.

XHTML+RDFa: This extension to XHTML takes advantage of the ability to add modules to the base XHTML 1.1 specification. It integrates into XHTML 1.1 attributes as defined in RDFa Core 1.1: Syntax and processing rules for embedding RDF through attributes. The W3C has used this extension itself. [View source of XHTML™ Modularization 1.1 - Second Edition as an example of a page using this document type.] The compilers of this resource are not aware of the degree to which the XHTML+RDFa document type has been used by others. Comments welcome.

XHTML 1.1 was published as a W3C Recommendation on May 31, 2001. It is based on XHTML 1.0 Strict, with minor changes. The specification and the DTD were reformulated using modules in the W3C Recommendation Modularization of XHTML, which was published on April 10, 2001.

The W3C XHTML2 Working Group was wound up without completing work on a version planned to follow XHTML 1.1. A draft specification for XHTML 2.0 was published as a Working Group Note, not a W3C Recommendation, in December 2010. The Wikipedia entry for HTML states, "XHTML 2.0 was incompatible with XHTML 1.x and, therefore, would be more accurately characterized as an XHTML-inspired new language than an update to XHTML 1.x."

In July 2010, a post at IBM Developer Works entitled The XML flavor of HTML5 stated, "Browser vendors had been largely ignoring the W3C, and had formed the Web Hypertext Application Technology Working Group (WHAT WG) in order to evolve HTML, creating HTML5. Support for W3C XHTML was stagnant. The W3C first recognized the practicalities by providing a place to continue the HTML5 work, and it accepted defeat by retiring XHTML efforts in 2009. There's no simple way to assess whether or not this means the end of XHTML in practice. HTML5 certainly is not at all designed to be XML friendly, but it does at least give lip service in the form of an XML serialization for HTML, which, in this article, I'll call XHTML5." The author went on to point out a substantial number of problems with using XHTML5 as well as pointing out potential advantages in its use. It is clear is that the only successor to XHTML 1.1 for web pages that are valid XML is the XML serialization of HTML5.