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callout — A “called out” description of a marked Area
callout ::= ((calloutlist|glosslist|bibliolist|itemizedlist|orderedlist|segmentedlist|simplelist|variablelist|caution|important|note|tip|warning|literallayout|programlisting|programlistingco|screen|screenco|screenshot|synopsis|cmdsynopsis|funcsynopsis|classsynopsis|fieldsynopsis|constructorsynopsis|destructorsynopsis|methodsynopsis|formalpara|para|simpara|address|blockquote|graphic|graphicco|mediaobject|mediaobjectco|informalequation|informalexample|informalfigure|informaltable|equation|example|figure|table|msgset|procedure|sidebar|qandaset|task|productionset|constraintdef|anchor|bridgehead|remark|highlights|abstract|authorblurb|epigraph|indexterm|beginpage)+)
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                         Name  | 
                     
                         Type  | 
                     
                         Default  | 
                  
| arearefs | IDREFS | Required | 
A “callout” is a visual device for associating annotations with an image, program listing, or similar figure. Each location is identified with a mark, and the annotation is identified with the same mark. This is somewhat analagous to the notion of footnotes in print.
An example will help illustrate the concept. In the following example, the synopsis for the mv command is annotated with two marks. Note the location of the old and new filenames.
mvoldfilenewfile
               Somewhere else in the document, usually close by, a CalloutList
               provides a description for each of the callouts:
               
            
| 
                         The old filename. The mv
                           command renames the file currently called   | 
                  |
| 
                         The new filename. The mv
                           command changes the name of the old file to   | 
                  
               Each Callout contains an annotation for an individual
               callout or a group of callouts. The Callout points to the
               areas that it annotates with ID references.
               The areas are identified by coordinates in an an Area or
               AreaSet, or by an explicit CO element.
               
            
Formatted as a displayed block.
                  CallOuts usually generate text that points the reader to
                  the appropriate area on the object being augmented. Often, these are
                  numbered bullets or other distinct visual icons. The same icons should
                  be used in both places. In other words, whatever identifies the callouts
                  on the object should generate the same icons on the respective
                  callouts.
                  
               
In online environments, it may also be possible to establish a linking relationship between the two elements.
                  The processing expectations of Callouts are likely
                  to deserve special consideration for interchange.  See Appendix F, Interchanging DocBook Documents.  This is especially true if your
                  interchange partners are producing documentation in a medium
                  that has restricted visual presentation features, such as aural
                  media or Braille.
                  
               
The following elements occur in callout:
                  abstract, address, anchor, authorblurb, beginpage, bibliolist, blockquote, bridgehead, calloutlist, caution, classsynopsis, cmdsynopsis, constraintdef, constructorsynopsis, destructorsynopsis, epigraph, equation, example, fieldsynopsis, figure, formalpara, funcsynopsis, glosslist, graphic, graphicco, highlights, important, indexterm, informalequation, informalexample, informalfigure, informaltable, itemizedlist, literallayout, mediaobject, mediaobjectco, methodsynopsis, msgset, note, orderedlist, para, procedure, productionset, programlisting, programlistingco, qandaset, remark, screen, screenco, screenshot, segmentedlist, sidebar, simpara, simplelist, synopsis, table, task, tip, variablelist, warning.
               
                        AreaRefs must point to one or more
                        callouts. Callouts can be identified with
                        Area or AreaSet elements in a
                        GraphicCO,
                        MediaObjectCO,
                        ProgramListingCO, or
                        ScreenCO element or with a simple
                        CO element in a number of other environments.
                        These callouts identify the
                        portions of the object described by this Callout.