Section 4.1:
The VALUE match type may be used with any comparator which returns
sort information.
And which comparator of the base language does that? All, I guess,
but I miss reading that.
"relational" draft is not the place for listing such comparators. There
is a separate document (currently draft-newman-i18n-comparator-05.txt)
that defines the comparator registry.
I guess you are right that duplicating information is not good, but the
Sieve base language contains so few comparators, that it would be nice
to state that those return sort information.
After all, "i;ascii-numeric" is described to allow at least 32 bit
integers and not being capable to compare signed numbers. The latter
at least is duplicated information, yet it is very helpful.
Michael