Name
programlistingco — A program listing with associated areas used in callouts
Synopsis
programlistingco ::=
(info? db.titleforbidden.info,
areaspec, programlisting,
calloutlist*)
Description
Callouts, such as numbered bullets, are an annotation mechanism. In an online system, these bullets are frequently “hot,” and clicking on them sends you to the corresponding annotation.
A programlistingco is a wrapper around an
areaspec and a programlisting. An
areaspec identifies the locations (coordinates) in
the programlisting where the callouts occur. The
programlistingco may also contain the list of
annotations in a calloutlist, although the
calloutlist may also occur outside the wrapper,
elsewhere in the document.
It is also possible to embed co elements
directly in the verbatim text, in order to avoid having to calculate the
correct coordinates. If you decided to go this route, use a programlisting and a
calloutlist without the
programlistingco wrapper. A programlistingco must specify at least
one coordinate.
For a complete description of callouts, see
callout.
Processing expectations
Formatted as a displayed block. This element is displayed “verbatim”; whitespace and line breaks within this element are significant.
The mandatory processing expectations of a
programlistingco are minimal: a system is expected
to render the program listing and the callout list, if present.
If explicit co elements are embedded in a
programlisting, they must generate appropriate
callout marks.
In online environments, the processing system may be able to instantiate the linking relationships between the callout marks in the program listing and the annotations. Some systems may even be able to go a step further and generate the callout marks automatically from the coordinate information, but this level of sophistication is not mandatory.
Examples
<article xmlns='http://docbook.org/ns/docbook'>
<title>Example programlistingco</title>
<programlistingco>
<areaspec>
<areaset xml:id="ex.plco.const">
<area xml:id="ex.plco.c1" coords='4'/>
<area xml:id="ex.plco.c2" coords='8'/>
</areaset>
<area xml:id="ex.plco.ret" coords='12'/>
<area xml:id="ex.plco.dest" coords='12'/>
</areaspec>
<programlisting>
sub do_nothing_useful {
my($a, $b, $c);
$a = new A;
$a->does_nothing_either();
$b = new B;
$c = "frog";
return ($a, $c);
}
</programlisting>
<calloutlist>
<callout arearefs="ex.plco.const">
<para>These are calls to the constructor
<function>new</function> in the object classes.
</para>
</callout>
<callout arearefs="ex.plco.ret">
<para>This function returns a two-element list.
</para>
</callout>
<callout arearefs="ex.plco.dest">
<para>The <emphasis>destructor</emphasis>
(<function>DESTROY</function>) for the object
<literal>$b</literal> will be called automatically
for this object since there can be no other references
to it outside this function.
</para>
</callout>
</calloutlist>
</programlistingco>
</article>sub do_nothing_useful {
my($a, $b, $c);
$a = new A; 
$a->does_nothing_either();
$b = new B;
$c = "frog";
return ($a, $c); 
}