In the abstract syntax,
for the repetition notation described in [RFC:3.6] and [RFC:3.7]
and by rule repeat in [RFC:4],
we use pairs of (i) natural numbers and (ii) natural numbers plus infinity.
A specific repetition [RFC:3.7] is abstracted
to a variable repetition [RFC:3.6] with the same minimum and maximum.
A repetition with a missing lower bound is abstracted
to one with the default (i.e. 0) as lower bound.
A repetition with a missing upper bound is abstracted
to one with the default (i.e. infinity) as explicit upper bound.
The notion of well-formed repetition ranges requires the minimum not to exceed the maximum.
