Information AboutXhtml |
| CATEGORIES ABOUT XHTML | |
| html | |
| markup languages | |
| w3c standards | |
| xml-based standards | |
The ''Extensible HyperText Markup Language'', or '''XHTML''', is a Markup Language that has the same depth of expression as HTML , but also conforms to XML syntax. Whereas HTML is an application of SGML , a very flexible markup language, XHTML is an application of XML , a more restrictive subset of SGML. Because they need to be Well-formed , true XHTML documents allow for automated processing to be performed using standard XML tools—unlike HTML, which requires a relatively complex, lenient, and generally custom Parser . XHTML can be thought of as the intersection of HTML and XML in many respects, since it is a reformulation of HTML in XML. XHTML 1.0 became a World Wide Web Consortium (W3C) Recommendation on January 26 , 2000 . XHTML 1.1 became a W3C recommendation on May 31 , 2001 . OVERVIEW ]] XHTML is the successor to HTML. As such, many consider XHTML to be the current or latest version of HTML. However, XHTML is a separate recommendation; the W3C continues to recommend the use of XHTML 1.1, XHTML 1.0, and HTML 4.01 for web publishing, and HTML 5 is currently being actively developed. Motivation The need for a reformulated version of HTML was felt primarily because World Wide Web content now needs to be delivered to many devices (like Mobile Device s) apart from traditional Computer s, where extra resources cannot be devoted to support the additional complexity of HTML syntax. In practice, however, HTML supporting browsers for constrained devices have emerged faster than XHTML support has been added to the desktop browser with the largest market share. Another goal for XHTML and XML was to reduce the demands on parsers and user-agents in general. With HTML, user-agents increasingly took on the burden of “correcting” errant documents. Instead XML requires user-agents to signal a “fatal” error when encountering malformed XML. This means that an XHTML browser can theoretically omit error recovery code even though it may even need slightly more error detection checks. The recommendation for browsers to post an error rather than attempt to render malformed content should help eliminate malformed content. Even when authors do not validate code, and simply test against an XML browser, critical errors will be revealed. An especially useful feature XHTML inherits from its XML underpinnings is XML Namespaces . With namespaces, authors or communities of authors can define their own XML elements, attributes and content models to mix within XHTML documents. This is similar to the semantic flexibility of the ‘class’ attribute from HTML, but with much more power. Some W3C XML namespaces/schema that can be mixed with XHTML include MathML for semantic math markup, Scalable Vector Graphics for markup of vector graphics, and RDFa for embedding RDF data. Relationship to HTML HTML is the antecedent technology to XHTML. The changes from HTML to first-generation XHTML 1.0 are minor and are mainly to achieve conformance with XML. The most important change is the requirement that the document must be Well-formed and that all Elements must be explicitly closed as required in XML. In XML, all element and attribute names are case-sensitive, so the XHTML approach has been to define all tag names to be lowercase. This contrasts with some earlier established traditions which began around the time of HTML 2.0, when many used uppercase tags. In XHTML, all attribute values must be enclosed by quotes (either 'single' or "double" quotes may be used). In contrast, this was sometimes optional in SGML, and hence in HTML, where numeric or boolean attributes can dispense with quotes (quoted attributes are assumed to be strings). All elements must also be explicitly closed, including empty (aka Singleton ) elements such as img and br. This can be done by adding a closing slash to the start tag: selected” contains no explicit value; instead, use HTML elements which are optional in the content model, will not appear in the DOM tree unless they are explicitly specified. For example, an XHTML page ''must'' have a |
|
|