There are files supporting the generation of PDF and
the typesetting of stuff that looks like math.
What this MIGHT mean is that we can use lisp programs
to compute the actual size of math expressions in TeX-like
notation, and use this feedback to do line=breaking.
My own (limited) experience with breqn was that it
didn't work very well.
Persons interested in this can look at cl-pdf and cl-typesetting
downloads / see google.
RJF