XHTML 1.0 Transitional Programming Help
XHTML 1.0 transitional is a language that combines XML (extensible markup language) and HTML (hypertext markup language). XHTML transitional is one of three standard XHTML documents defined by the World Wide Web Consortium and was designed to bring consistency and standards to web page code. The transitional language declaration allows limited presentational elements in web pages, as well as certain deprecated HTML elements. It is considered less robust than the strict language declaration.
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History
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The World Wide Web Consortium (W3C) considers XHTML "a reformulation of HTML 4.0 as an application of the Extensible Markup Language (XML)." Scientists originally developed HTML as a way to exchange documents among themselves; however, it has been widely adopted for other purposes, many of which are outside of HTML's original design intent. This has led to stretching of the language and resulted in nonstandard HTML that is impossible for some user-agents to understand. Adding XML standards, such as XHTML transitional to HTML, makes it extensible and portable.
DTDs
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The XHTML 1.0 standard defines three DTDs, or Document Type Definitions. Each DTD targets a different detail level for the document's XHTML and specifies the web page's syntax in Standard Generalized Markup Language (SGML). The DTD exactly describes the document's allowed syntax. The three XHTML DTDs are "strict," "transitional," and "frameset." The strict DTD is used for clean markup with no presentational elements. The transitional DTD allows some presentational elements and the frameset DTD allows the use of HTML frames.
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Purpose
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The XHTML 1.0 transitional DTD contains all HTML presentation and deprecated elements. According to the W3C, the purpose of this DTD is "to take advantage of XHTML features including style sheets but nonetheless to make small adjustments to your markup for the benefit of those viewing your pages with older browsers which can't understand style sheets." The ultimate goal of the XHTML standard was document conversion to the strict DTD, which provides consistency in cross-browser and cross-platform applications.
Namespaces
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XHTML transitional documents, like all XML documents, can contain any XML elements that the developer decides to implement. However, if attributes are used that have the same name but different meanings, there will be a meaning conflict. Namespaces qualify elements and attributes used in XML by identifying them with a specific http uniform resource identifier (URI). XHTML transitional markup indicates the transitional DTD as the root, but allows the inclusion of other DTDs in XHTML (XML) documents.
Rules
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XHTML 1.0 transitional documents have a set of rules that must be followed in order for the document to be considered valid XHTML. When applied to HTML, these rules provide a basic standard. For example, all XHTML elements must be properly nested and all XHTML elements must be in lowercase. All XHTML elements must be properly closed, including empty elements, such as break <br/> elements. All XHTML documents must have one root element, typically the <html> element.
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References
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