FLD "required" vs "expected" to be used for all RIF logic dialects

FLD says "All logic-based RIF dialects are required to be derived from
RIF-FLD by specialization" and several variants of that notion appear
elsewhere in FLD and UCR (and possibly elsewhere, that I didn't notice).

I don't really undertand what this constraint is trying to do.  Is it a
promise that all future logic dialects from RIF-WG *will* use FLD?  Is
it some kind of constraint on vendor extensions?  I don't think it's
right for us to say either one here.

I'm fine with conveying expectation, like: "Logic-based RIF dialects
are expected to be derived from RIF-FLD by specialization".  Okay?

      -- Sandro