This example is an extract from the index of a PDF file:

...

<IDF FILENAME="IDF.pdf">

...

<GROUP INDEX="About IDF syntax" PAGE="15">
 <GROUP INDEX="Dimensions in IDF" PAGE="15"/>
 <GROUP INDEX="Notes on text" PAGE="15"/>
 <GROUP INDEX="Using data fields" PAGE="16"/>

</GROUP>

...

<PAGE PAGE="15"><INCLUDE/></PAGE>
<PAGE PAGE="16"><INCLUDE/></PAGE>

...

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Three topics (Dimensions in IDF, Notes on text, Using data fields) are contained within a parent group (About IDF syntax) shown in an open folder.

Folders may be opened and closed with a double-click of the mouse.