full text search: the concept of a "word"

I'm considering using tsearch2 in the project I'm working on right
now...however, I'm not sure if tsearch2 can handle my very specific
requirements - I therefore hope someone can tell me if the following
is possible and how I should go about it...

My textfields are trigger-generated using information from a number of
tables: these fields can be, say, a couple of thousand characters
wide.
Up to here, there's no problem.
What I'd like to do is define - possibly using regexps - what
constitutes a word. For instance, my word separator is a semicolon,
not a space; a dash is not a separator, and neither are language
specific characters (which might be interpreted that way by a language
agnostic tool)...
BTW, I use UTF-8 as my database encoding if it's of any importance.

What it comes down to is this: is it possible to somehow define what
constitutes a word?

TIA,
Tomislav