HTML and CSS Reference
1.5. Standards and Extensions
The basic syntax and semantics of HTML are defined in the HTML stand-
ard, now in its final version, 4.01. HTML matured quickly, in barely a dec-
ade. At one time, a new version would appear before you had a chance
to finish reading an earlier edition of this topic. Today, HTML has stopped
evolving. As far as the W3C is concerned, XHTML has taken over. Now
the wait is for browser manufacturers to implement the standards.
The XHTML standard currently is version 1.0. Fortunately, XHTML version
1.0 is, for the most part, a reconstitution of HTML version 4.01. There are
some differences, which we explore in Chapter 16 . The popular browsers
continue to support HTML documents, so there is no cause to stampede
to XHTML. Do, however, start walking in that direction: a newer XHTML
version, 2.0, is under consideration at the W3C, and browser developers
are slowly but surely dropping nonstandard HTML features from their
Obviously, browser developers rely upon standards and accepted con-
ventions to have their software properly format and display common
HTML and XHTML documents. Authors use the standards to make sure
they are writing effective, correct documents that get displayed properly
by the browsers.
However, standards are not always explicit; manufacturers have some
leeway in how their browsers might display an element. And to complic-
ate matters, commercial forces have pushed developers to add into their
browsers nonstandard extensions meant to improve the language.
Confused? Don't be: in this topic, we explore in detail the syntax, se-
mantics, and idioms of the HTML version 4.01 and XHTML version 1.0
languages, along with the many important extensions that are supported
in the latest versions of the most popular browsers.