Webmaster in a Nutshell, Third Edition

XML Reference

Now that you have had a quick taste of working with XML, here is an overview of the more common rules and constructs of the XML language.

Well-Formed XML

These are the rules for a well-formed XML document:

• All element attribute values must be in quotation marks.

• An element must have both an opening and a closing tag, unless it is an empty element.

• If a tag is a standalone empty element, it must contain a closing slash (/) before the end of the tag.

• All opening and closing element tags must nest correctly.

• Isolated markup characters are not allowed in text; < or & must use entity references. In addition, the sequence ]]> must be expressed as ]]> when used as regular text. (Entity references are discussed in further detail later.)

• Well-formed XML documents without a corresponding DTD must have all attributes of type CDATA by default.

Special Markup

XML uses the following special markup constructs.

Element and Attribute Rules

An element is either bound by its start and end tags or is an empty element. Elements can contain text, other elements, or a combination of both. For example:

<para>
   Elements can contain text, other elements, or
   a combination. For example, a chapter might 
   contain a title and multiple paragraphs, and 
   a paragraph might contain text and 
   <emphasis>emphasis elements</emphasis>.
</para>

An element name must start with a letter or an underscore. It can then have any number of letters, numbers, hyphens, periods, or underscores in its name. Elements are case-sensitive ...