calloutlist element question

To 
whom it may concern,

 

I am 
unclear of the <calloulist> element and it's function. I am fairly 
new to docbook and xml, so I am not sure if this is something common to 
programmers. Specifically, what is a "calloutlist", a "callout" and what is the 
meaning of the "arearefs" attribute? 

 

The following definition for calloutlist was found at 
the docbook.org site, but it is unclear to me: calloutlist: A CalloutList is 
a list of annotations or descriptions. Each Callout points to 
the area on a Graphic, ProgramListing, 
or Screen that 
it augments. 

 

Here is an example in 
code:

<chapter>

    <title>Example</title>

        
<calloutlist>

            
<callout arearefs=""></callout>

        
</calloutlist>

</chapter>

 

Help would be much 
appreciated.

Thanks.

René