Purpose of mk/find-prefix.mk

["J. Lewis Muir" <jlmuir%imca-cat.org@localhost>]

Hello, pkgsrc experts!

I've noticed some packages (e.g. editors/OmegaT) use mk/find-prefix.mk
to find the installation prefix of a particular package (e.g.
devel/apache-ant) while others (e.g. devel/opengrok) just assume an
installation prefix of a particular package (e.g. devel/apache-ant) to
be "${PREFIX}".  What is the reason for using mk/find-prefix.mk instead
of "${PREFIX}"?

I might guess the following reason: if a package dependency, let's say
devel/apache-ant, were satisfied as a "built-in" package, that package
would reside outside of the pkgsrc PREFIX directory and therefore
"${PREFIX}/bin/ant" wouldn't work.  Is this the main reason?  Are there
other reasons?

Thank you!

Lewis