Web Design in a Nutshell, 3rd Edition

XML Document Syntax

Now let’s look at some of the particulars of XML syntax using this simple XML document:

<?xml version="1.0" encoding="US-ASCII" standalone="no"?>
<!DOCTYPE accounts SYSTEM "simple.dtd">
<accounts>
<customer>
    <name>
        <firstname>Bobby</firstname>
        <lastname>Five</lastname>
    </name>
    <accountNumber>4456</accountNumber>
    <balance>111.32</balance>
</customer>
<!-- more customers will be added soon -->
<?php  print date ('Fj,Y') ?>
</accounts>

Well-Formed Versus Valid

In short, well-formed documents comply with the rules for marking up documents according to XML , independent of a specific language. For instance, all elements must be correctly nested and may not overlap.

Valid documents are well-formed and abide by the rules of a DTD for a particular XML language. For instance, in XHTML, it is invalid to put a body element in an a element.

An XML document must be well-formed, and should be valid , but validity is not required.

Tip

Because XHTML is an XML application, all of the following syntax conventions apply to web documents written in XHTML.