HTML and CSS Reference
Why bother with a markup metalanguage? Because, as the familiar pro-
verb goes, the W3C wants to teach us how to fish so that we can feed
ourselves for a lifetime. With XML, there is a standardized way to define
markup languages for different needs, instead of having to rely upon
HTML extensions. Mathematicians need a way to express mathemat-
ical notations, for instance; composers need a way to present music-
al scores; businesses want their web sites to take sales orders from
customers; physicians look to exchange medical records; plant man-
agers want to run their factories from web-based documents. All of
these groups need an acceptable, resilient way to express these differ-
ent kinds of information so that the software industry can develop the
programs that process and display these diverse documents.
XML provides the answer. Each content sectorthe business group, the
factory-automation consortium, a trade associationmay define a markup
language that suits their particular need for information exchange and
processing over the Web. Computer programmers then create XML-
compliant processesparsersthat read the new language definitions and
allow the server to process the documents of those languages.
15.1.1. Creation Versus Display
While there is no limit to the kinds of markup languages that you can
create with XML, displaying your documents may be more complicated.
For instance, when you write HTML, a browser understands what to do
with the <h1> tag because it is defined in the HTML DTD.
With XML, you create the DTD. [*] For example, wouldn't a recipe DTD be
a great way to capture and standardize all those kumquat recipes you've
been collecting in your kitchen drawers? With special <ingredient> and
<portion> tags, the recipes are easy to define and understand. However,
browsers won't know what to do with these new tags unless you attach
a stylesheet that defines their handling. Without a stylesheet, XML-com-
pliant browsers render these tags in a very generic waycertainly not the
flourishing presentation your kumquat recipes deserve.