XHTML 1.0 is the current version supported by the World Wide Web Consortium (W3C), which is the standards governing body for the XHTML specification. Version 1.1 is currently being developed, at the time of writing this guide.
XHTML is HTML written according to the XML rules of well-formed ness. As we said in our introduction XHTML stands for the Extensible Hyper Text Markup Language.
It provides the bridge for web designers to enter the web of the future, while still being able to maintain compatibility with today's HTML 4 browsers. A reformulation of HTML 4 as an application of XML, and very much like HTML 4, with a few notable exceptions. XHTML should and is easy to learn.
XHTML is modular, making it easy to combine with mark-up tags for things like vector graphics, multimedia, math, e-commerce and more. Content providers will find it easier to produce data for a wide range of platforms, with better assurances as to how the content is rendered.
The modular design reflects the realisation that a one-size-fits-all approach will no longer work in a world where browsers vary enormously in their abilities.
The key points of XHTML are:
Element and attribute names must be written in lowercase.
Elements must nest, no overlapping
All non-empty elements must be closed
Empty elements must be terminated
Attribute values must be quoted
To understand XHTML, it is best to understand XML:The revolution
and bridging language of all machine languages.