optional dependencies

[Tjong-A-Hung]

Dear all,

for quite some time I have been annoyed by the fact that alot of ports seem to install so called dependencies which *I* don't need.
An example is a port needs a pdfviewer, I have acroread installed. Someone may think xpdf or kpdf is better. All of that is besides the point.
If the port needs a pdfviewer and I have *my* favourite pdf viwer installed, don't install the pdfviewer *you* think is best.
Isn't it possible to add optional dependencies like:
look if he has kpdf/xpdf/acroread, if so do not install the pdfviewer. configure the app in such a way that it does use this pdfviewer I already have installed.
And if not install *your* choice of pdfviewer.

texmaker is one of these ports where this doesn't happen as I would like it to.

I have read up on the porters handbook to see if it was possible, but the only thing I could find was the following:
http://www.freebsd.org/doc/en_US.ISO8859-1/books/porters-handbook/makefile-depend.html

This however doesn't provide enough information to me to create a dependency the way I would like it too.
Is there someone in the community who can give me a clue of what I *can* do?

Regards, Gabor