Re: bookmarks for concept index

[Stephen Gildea]

>   @require @newcommand
>   @newcommand
>   stuff
>   @end require

I like it.  @require could also be a hook for loading extensions or
less-often-used commands.

You could add an argement saying what to do if @newcommand cannot be
found: whether to ignore the body or to abort processing the document.