Expressing an "either this or that"-dependency (libwww-perl/p5-HTTP-Cookies)

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

Suppose I have a Perl module or script use'ing HTTP::Cookies (at some low 
enough version).
Versions of libwww-perl up to 5.x included this module, from 6.x on it's 
separate.
The factored-out versions therefore conflict with p5-libwww<6.0.
Suppose we are going to have libwww-perl 6.x in some versions of pkgsrc and 5.x 
in others and I want to be compatible with both of them.

So I either need p5-HTTP-Cookies or libwww-perl<6.0.

How do I turn this into a DEPENDS? Writing

DEPENDS+=       {p5-libwww<6.0,p5-HTTP-Cookies>=x.yy}:../../www/p5-HTTP-Cookies

will only work if p5-libwww 5.x has already been installed.
Should I have two separate DEPENDS depending on the underlying pkgsrc 
supporting p5-libwww 5.x resp. 6.x?