[O] execute function when TAB expands a headline

[Christian Wittern]

Hi there,

I am (also!) using org-mode for displaying dictionary data, with the
headword part of the headline.  When I press on TAB, the entry expands and I
see the explanation and some sample sentences.  Now, to make it easier (for
my eyes) to parse the examples, I would like to highlight the headword, as
it appears in the examples.  I believe hi-lock mode etc. could do the trick,
but I am stuck at how to hook into the TAB execution, so that I can call my
code.  Any hints very much appreciated!

All the best,

Chris