Roleset complement.01 Verbnet Class: NONE "go well with, fill out":

Roles:

Arg1:thing complementing


Arg2:thing complemented

Examples:

person: ns tense: present aspect: ns voice: active form: full


this and that (-)
The maker of telecommunications and defense equipment said Carol Cable's portfolio and market focus would complement the company's current wire and cable businesses.
Arg1:	Carol Cable's portfolio and market focus
ArgM-MOD:	would
REL:	complement
Arg2:	the company's current wire and cable businesses

I have a vague intuition that complement might take an agent at some point, hence starting arg numbering at 1. And even if no agent ever appears, it seems weird to call the first half of a complementary pair the arg0, since it's not agentive.