HTML & XHTML: The Definitive Guide, 6th Edition

Grammatical Conventions

We use a number of typographic and punctuation conventions to make our grammar easy to understand.

Typographic and Naming Conventions

For our grammar, we denote the terminals with a monospaced typeface. The nonterminals appear in italicized text.

We also use a simple naming convention for the majority of our nonterminals: if a nonterminal defines the syntax of a specific tag, its name is the tag name followed by _tag. If a nonterminal defines the various language elements that may be nested within a certain tag, its name is the tag name followed by _content.

For example, if you are wondering exactly which elements are allowed within an <a> tag, you can look for the a_content rule within the grammar. Similarly, to determine the correct syntax of a definition list created with the <dl> tag, look for the dl_tag rule.

Punctuation Conventions

Each rule in the grammar starts with the rule’s name, followed by the replacement symbol (::=) and the rule’s value. We’ve intentionally kept the grammar simple, but we do use three punctuation elements to denote alternation, repetition, and optional elements in the grammar.

Alternation

Alternation indicates a rule may actually have several different values, of which you must choose exactly one. Pipes (|) separate the alternatives for the rule.

For example, the heading rule is equivalent to any one of six HTML heading tags, so it appears in the table as:

heading                  ::=      h1_tag
                         |        h2_tag
                         |        h3_tag
                         |        h4_tag
                         |        h5_tag
                         |        h6_tag

The heading ...