How can I use the negation within square brackets as an exception, to find e. g. everything between a-z except for the the range from m-o?
By the way: it's not for the sake of this example that I ask, but to be able to exclude ranges within ranges, or even single letters within ranges. I am pretty much aware that in this example it can be calculated.
I use the Zend engine (PHP).
You should be able calculate the difference yourself.
If the regex engine supports lookahead assertion, you could use
but this would probably be less efficient.