KILL IE6

02 CSS and XHTML

HTML 4.01 is the final HTML version. Future work by the W3C is being done on XHTML, which is based on XML. XML is a universal markup language that can be used to define specific markup, such as XHTML, or DocBook. XML markup is well-defined by a schema.
XHTML redefines HTML in terms of XML, whileas HTML was based on the older SGML. XML itself is a reformulation of SGML. Complex fun, huh? XHTML is not a new markup language, but builds on HTML. Moving from valid HTML to XHTML is quite simple.

From HTML to XHTML

Doctypes are a key element of valid web pages.

• The !DOCTYPE processing instruction needs to be present at the beginning of an XHTML document.
• All tags in XHTML are lowercase.
• Attribute values need to be quoted. Shorthand for attributes does no longer work: "checked" is no longer allowed, you have to use checked="checked" or selected="selected"
• All tags in XHTML need to be closed, whether they contain text like <td> &#160 </td>, or whether they don't, such as
  <hr />
  <br />
  <input ... />
  <meta ... /> ...
• Special encoding, such as the windows encoding, should be changed to UTF-8.
• Presentational markup such as <b>- and &<i>-is deprecated and should be replaced with <strong>- and <em>

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