Structural Layer
After years of browser developers getting jiggy with tag creation, the web community is returning to HTML’s original intent as a markup language: to describe the structure of the document, not to provide instructions for how it should look. The structural markup of the document forms the foundation on which the presentational and behavioral layers may be applied.
These are the current standard languages for structural markup:
- XHTML 1.0 (Extensible Hypertext Markup Language) and XHTML 1.1
XHTML 1.0 is simply HTML 4.01 rewritten according to the stricter syntax rules of XML. XHTML 1.1 finally does away with deprecated and legacy elements and attributes and has been modularized to make future expansions easier. XHTML 2.0 is currently in development. The last version of HTML was HTML 4.01, which is still universally supported by today’s browsers, but is not forward compatible. Part II looks at these languages in detail. Links to the full XHTML 1.0, XHTML 1.1, and HTML 4.01 specifications can be found on this page: http://www.w3.org/MarkUp/.
- XML 1.0 (Extensible Markup Language)
XML is a set of rules for creating new markup languages. It allows developers to create custom tag sets for special uses. See Chapter 7 for more information, or go to the source at http://www.w3.org/XML/.
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