[Typo3-dev] indexsearch - extending or rebuilding?

[dan frost]

I'm just about to start on either an extension or a rebuild of index 
search. I need it to add other things to the search and to filter by 
other things (in this case, legislation mentioned in a document).

Has anyone done stuff like this before? How has any of you changed index 
search to customise it - that is, why do you change it?

I ask this because it would be better for me to make something re-useable.

dan