HTML and CSS Reference
In-Depth Information
For example, the
heading
rule is equivalent to any one of six HTML head-
ing tags, so it appears in the table as:
::=
heading
h1_tag
|
h2_tag
|
h3_tag
|
h4_tag
|
h5_tag
|
h6_tag
The
heading
rule tells us that wherever the
heading
nonterminal appears
in a rule, you can replace it with exactly one of the actual heading tags.
A.1.2.2. Repetition
Repetition indicates that an element within a rule may be repeated
some number of times. Repeated elements are enclosed in curly braces
(
{...}
). The closing brace has a subscripted number other than 1 if the
element must be repeated a minimum number of times.
For example, the
<ul>
tag may contain only
<li>
tags, or it may be
empty. The rule, therefore, is:
::= <ul>
{
li_tag
}0
</ul>
ul_tag
This rule says that the syntax of the
<ul>
tag requires the
<ul>
tag and
zero or more
<li>
tags, followed by a closing
</ul>
tag. We spread this
rule across several lines and indented some of the elements to make
it more readable; your documents need not actually be formatted this
way.
