FreeBSD Ports vs. Gentoo Portage (a matter of concept)

[Norberto Meijome]

Parv wrote:
> in message <dsav13$99q$1 at sea.gmane.org>, wrote martinko thusly...
>> Norberto Meijome wrote:
>>> Hans Nieser wrote:
>>>
>>>> FreeBSD Prospect wrote:
> ...
>>>> What I am especially fond of in portage is the USE-flags and the
>>>> way you can specify then globally and individually for each
>>>> package and how you can get a nice, short overview of which
>>>> USE-flags a package uses and which of them are enabled with
>>>> "emerge -pv port".
> ...
>> there are global USE-flags in FreeBSD too and you also can
>> configure ports individually, but i'd agree that Gentoo way is
>> more transparent.
> 
> Those USE_* flags are for port creators/maintainers not
> users/installers; user use of, well, USE_* flags may get you in a
> trouble.  OTOH, WITH_* & WITHOUT_* flags lie in user domain.
> 
>   - Parv
> 


interesting. Is there anywhere one can read about these things, ie,
about where and how USE_* are used/ defined, WITH_, etc. ... and how to
compile a list of available (USE|WITH)_* and their meaning (grep -r
USE|WITH /usr/ports/*/*/Makefile ?? )... so far i've been using the
@freebsd.org lists to do this, but it's rather unreliable and unsystematic
B