HTML and CSS Reference
elements, for an XML document to be valid, every tag must be closed, every attribute
must have a value, and more. XHTML 1.1 requires that HTML documents also be valid
Technically, XHTML 1.1 and HTML 4.01 are very similar. The tags and attributes are
almost the same, but a few simple rules have to be followed to make sure that a docu-
ment complies with the XHTML 1.1 specification. Throughout this topic, I explain how
to deal with the different HTML tags to ensure that your pages are readable and still look
good in all kinds of browsers.
The W3C HTML Working Group is busy creating a new standard for HTML: HTML5.
The goal of HTML5 is to introduce new elements that more accurately reflect the state of
the Web as it exists now. These elements include things like <header> and <footer> for
the page header and footer, respectively.
HTML5 does not demand that web pages be valid XML, relaxing some of the rules that
XHTML 1.0 imposed. However, today's valid HTML or XHTML will still be valid in
HTML5 when it's fully adopted.
Most browsers have already begun to support the new features in HTML5, even though
the specification has not been finalized. I'll explain what you can do with HTML5 now
and what you'll need to do as browser support for HTML5 expands.
One of the most important differences between HTML5 and earlier HTML specifications
is that HTML5 is being created with the cooperation of the browser makers. In the past,
support for HTML specifications among browser vendors has been uneven at best. Only
features that the browser vendors have committed to support will be included in HTML5.
If agreement cannot be reached on a particular feature, that feature will not be included
in a specification. The hope is that at the end of the HTML5 process, web developers
will have a specification they can count on to work from.
Finally, HTML5 removes many elements that had been introduced in previous standards
but are now superseded by Cascading Style Sheets. Some of these tags were deprecated
in previous standards—HTML5 drops them entirely.
Pages written in HTML are plain text files (ASCII), which means that they contain no
platform- or program-specific information. Any editor that supports text (which should