XHTML, Extensible Hypertext Markup Language

7 Sep

Extensible Hypertext Markup Language (XHTML), or
simply XTML, is a markup language that has the same
expressive possibilities as HTML, but conforms to
the XML standard which is more strict. This also
allows it to be extended more easily without
breaking existing implementations. XHTML 1.0 became
a World Wide Web Consortium (W3C) Recommendation on
January 26, 2000.

XHTML is the successor to and the current version
of HTML. The need for a more strict version of HTML
was felt primarily as now web content needs to be
delivered to many other devices (like mobile
devices) apart from traditional computers, where
extra resources cannot be devoted to support the
generosities of HTML (for example, support for both
upper-case and lower-case elements). The XHTML DTD
is defined within the XML DTD to enforce the strict
rules of XML.

Most of the recent versions of popular web browsers
render XHTML properly, and many older browsers will
also render XHTML as it is mostly a subset of HTML
and most browsers do not require valid HTML.
Similarly, almost all web browsers that are
compatible with XHTML also render HTML properly.
Some say this is slowing the switch from HTML to
XHTML.

XHTML’s true power is realized when used in
conjunction with Cascading Style Sheets. This makes
the separation of content and form an integral part
of the web page’s code.

The changes from HTML, to transitional XHTML, are
minor, and are mostly just in conformance with XML.
The most important change is the requirement that
all HTML tag|tags are well-formed tag|well-formed.
Additionally, in XHTML, all elements must be
lowercased. This is in direct contrast to
established traditions which began around the time
of HTML 2.0, when most people preferred uppercased
tags. In XHTML, all attributes, even numerical
ones, must be quoted. (This was mandatory in HTML
as well.) All tags must also be closed, even the
empty tags <img> and
<br>. This can be done by adding a
closing slash to the tag: <img />
and <br />. Attribute minimization
(e.g., <option selected>) is also
prohibited. More differences are detailed at the
[http://www.w3.org/TR/xhtml1/#diffs W3C XHTML
specification].

Versions of XHTML

XHTML is HTML reformulated as XML. There are three
different versions, equal in scope to their
respective HTML4.0 versions.

  • XHTML 1.0 Transitional: Intended for easy
    migration from HTML3.2, or for those using link
    targets or inline-frames
  • XHTML 1.0 Strict: Separates content from layout
    (which now moves to CSS)
  • XHTML 1.0 Frameset: For splitting the browser
    window into several HTML_tag#Frames
  • frames
  • XHTML 1.1: Module-based XHTML; authors can import
    additional features (such as framesets) into
    their markup. This version also allows for Ruby
    characters
  • ruby markup support, needed for Far-Eastern
    languages.
  • * XHTML Basic: A special “light” version of XHTML
    for devices which cannot use the full XHTML set,
    primarily used on handhelds such as mobile
    phones. This is the intended replacement for
    Wireless Markup Language
  • WML and C-HTML.
  • * XHTML Mobile Profile: Based on XHTML Basic,
    this Nokia effort targets hand phones
    specifically by adding mobile phone-specific
    elements to XHTML Basic

Work on XHTML 2.0 is, as of 2004, still underway.
The XHTML 2.0 draft is controversial because it
breaks backwards compatibility with all previous
versions, and is therefore in effect a new markup
language inspired by (X)HTML rather than a true
successor of it.

External Links

This article is licensed under the GNU
Free Documentation License. It uses material
from the
Wikipedia article “XHTML”.

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