Re: DOCBOOK: indexterm: primary is optional?

[Michael Smith <smith at xml-doc dot org>]

Brian Lalonde <brianiacus@yahoo.com> writes:

> I notice that the indexterm element is defined as:
> 
> indexterm ::=
> (primary?,
>  ((secondary,
>    ((tertiary,
>      (see|seealso+)?)|
>     see|seealso+)?)|
>   see|seealso+)?)
> 
> Why is primary optional?

I think that's necessary to allow for end-of-range Indexterms, which
need to be empty. For example:

    <indexterm class="startofrange" id="foo">
      <primary>bar</primary>
    </indexterm>

    ...range of content you want to index here...

    <indexterm class="endofrange" startref="foo"/>



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