Question about ports builds

[Charlie Sorsby]

Hello,

When one builds (or attempts to build) a port, does the Makefile
know about dependencies and, if necessary, fetch and build any 
that are needed but not found?

Thank you and kindest regards,

Charlie

PS It would be really helpful if each port/package at freebsd.org
had an indication whether it requires the latest and greatest
version of freeBSD.  Put another way, it would be nice to know the
oldest version of freeBSD it will work with.  Perhaps that could be
included in the "Requires" list on the page for the port/package.