What is the actual syntax used to FLAVOR ports?

[Chris]

OK I know FLAVOR is an evolving concept. But I can not find
the FLAVOR documentation. Only references in the porters
handbook. What I think needs to be available is an entire
list of flavor tags for all (port) categories.
For example;
make FLAVOR=python27 returns the error use py27.
OK now I know how to flavor, and build python flavors.
But what of Perl?
make FLAVOR=perl2.8. Nope. How about make FLAVOR=p5-28,
and so it goes...
Does there exist a definitive list of flavors? It'd
also be valuable for defining defaults in make.conf(5)

Thanks!

--Chris