HTML and CSS Reference
In-Depth Information
A.1.2.3. Optional elements
Some elements may appear in a document but are not required. Option-
al elements are enclosed in square brackets ( [. . .] ). The <table> tag,
for example, has an optional caption:
::= <table>
[ caption_tag ]
{ tr_tag }0
In addition, the rule says that a table begins with the <table> tag, fol-
lowed by an optional caption and zero or more table-row tags, and ends
with the </table> tag.
A.1.3. More Details
Our grammar stops at the tag level; it does not delve further to show
the syntax of each tag, including tag attributes. For these details, refer
to the quick-reference card included with this topic.
A.1.4. Predefined Nonterminals
The HTML and XHTML standards define a few specific kinds of content
that correspond to various types of text. We use these content types
throughout the grammar. They are:
Text is interpreted exactly as specified; no character entities or
style tags are recognized.
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