To use a markup language defined with XML, you should be able to read and understand the elements and entities found in its XML DTD. But don’t be put off: while XML DTDs are verbose, filled with obscure punctuation, and designed primarily for computer consumption, they are actually easy to understand once you get past all the syntactic sugar. Remember, your brain is better at languages than any computer is.
As we said previously, an
is a collection of XML entity and element declarations and comments.
Entities are name/value pairs that make the DTD easier to read and
understand, while elements are the actual markup tags defined by the
DTD, like HTML’s
<h1> tags. The DTD also describes the
content and grammar for each tag in the language. Along with the
element declarations, you’ll also find
attribute declarations that define the
attributes authors may use with the tags defined by the element
There is no required order, although the careful DTD author arranges declarations in such a way that humans can easily find and understand them, computers notwithstanding. The beloved DTD author includes lots of comments, too, that explain the declarations and how they can be used to create a document. Throughout this chapter, we use examples taken from the XHTML 1.0 DTD, which can be found in its entirety at the W3C web site. Although lengthy, you’ll find this DTD to be well-written, complete, and, with a little practice, easy to understand. ...