Java Reference
In-Depth Information
You're going to take a brief look now at the technologies and standards that have an impact on JavaScript
and fi nd out a little background information about each. Some of the technologies may be unfamiliar,
but you need to be aware of their existence at the very least.
HTML
The HTML standard is maintained by W3C. This standard might seem fairly straightforward, given
that each version should have introduced just a few new elements, but in reality the life of the standards
body was vastly complicated by the browser wars. The versions 1.0 and 2.0 of HTML were simple, small
documents, but when W3C came to debate HTML version 3.0, they found that much of the new func-
tionality it was discussing had already been superseded by new additions, such as the <applet /> and
<style /> elements, to the version 3.0 browser's appletstyle. Version 3.0 was discarded, and a new
version, 3.2, became the standard.
However, a lot of the features that went into HTML 3.2 had been introduced at the behest of the browser
manufacturers and ran contrary to the spirit of HTML, which was intended solely to defi ne structure.
The new features, stemming from the <font /> element, just confused the issue and added unneces-
sary presentational features to HTML. These features really became redundant with the introduction
of style sheets. So suddenly, in the version 3 browsers, there were three distinct ways to defi ne the style
of an item of text. Which was the correct way? And if all three ways were used, which style did the text
ultimately assume? Version 4.0 of the HTML standard was left with the job of unmuddling this chaotic
mess and designated a lot of elements for deprecation (removal) in the next version of the standards.
It was the largest version of the standard so far and included features that linked it to style sheets and
the Document Object Model, and also added facilities for the visually impaired and other unfairly
neglected minority interest areas. The current version of the HTML standard is 4.01.
XML
Extensible Markup Language, or XML, is a standard for creating markup languages (such as HTML). XML
itself has been designed to look as much like HTML as possible, but that's where the similarities end.
HTML is actually an application of the meta-language SGML, which is also a standard for generating
markup languages. SGML has been used to create many markup languages, but HTML is the only one
that enjoys universal familiarity and popularity. XML, on the other hand, is a direct subset of SGML.
SGML is generally considered to be too complex for people to be able to accurately represent it on a
computer, so XML is a simplifi ed subset of SGML. XML is also much easier to read than SGML.
XML's main use is for the creation of customized markup languages that are very similar in look and
structure to HTML. One main use of XML is in the representation of data. Whereas a normal database
can store information, databases don't allow individual stored items to contain information about their
structure. XML can use the element structure of markup languages to represent any kind of data in
which information contained in the structure might otherwise be lost, from mathematical and chemical
notations to the entire works of Shakespeare. For instance, an XML document could be used to record
that Mark Antony doesn't appear until Scene II Act I of Shakespeare's play
Julius Caesar,
whereas a rela-
tional database would struggle to do this without a lot of extra fi elds, as the following example shows:
<play>
<act1>
