Learning XML, 2nd Edition

Tags

If XML markup is a structural skeleton for a document, then tags are the bones. They mark the boundaries of elements, allow insertion of comments and special instructions, and declare settings for the parsing environment. A parser, the front line of any program that processes XML, relies on tags to help it break down documents into discrete XML objects. There are a handful of different XML object types, listed in Table 2-1.

Table 2-1. Types of tags in XML

Object	Purpose	Example
empty element	Represent information at a specific point in the document.	<xref linkend="abc"/>
container element	Group together elements and character data.	<p>This is a paragraph.</p>
declaration	Add a new parameter, entity, or grammar definition to the parsing environment.	<!ENTITY author “Erik Ray">
processing instruction	Feed a special instruction to a particular type of software.	<?print-formatter force-linebreak?>
comment	Insert an annotation that will be ignored by the XML processor.	<!— here’s where I left off —>
CDATA section	Create a section of character data that should not be parsed, preserving any special characters inside it.	<![CDATA[Ampersands galore! &&&&&&]]>
entity reference	Command the parser to insert some text stored elsewhere.	&company-name;

Elements are the most common XML object type. They break up the document into smaller and smaller cells, nesting inside one another like boxes. Figure 2-1 shows the document in Chapter 1 partitioned into separate elements. Each of these pieces has its own properties ...