[?] Use Except in a RegularExpression?

Friends:
Can Except be used in Regular Expressions? And then how?
This is potentially quite useful.
Suppose I want to match a pattern with the class character [A-Z] but without the class character [B-D].
This seems to be a job for combined regular expressions and Except…But then how to do it?
Any help is welcome,
Francisco

teststring=“adefghbchbcdecdbllbbbbo12c34bcbcbcyyy”;
StringCases[teststring, (Except[CharacterRange[“b”,“d”],CharacterRange[“a”,“z”]])..]

you don’t gain anything by using the regular expression

StringCases[teststring, RegularExpression["(?ms)(?:(?=[^bcd])[a-z])+"]]

Related:

This is excellent and works perfectly.

Sorry for the absurd delay in answering you kind feedback. This seems obviously rude. But it has an explanation. I simply stopped receiving notifications from the Wolfram community at my email box and completely forgot to come back.

I suddenly started getting notifications back, and here I am

So thanks again
Francisco