Consider the following set: [A-z]. Most likely it's an incorrect definition because the range

ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxy

contains nonimplied characters:

[\]^_`

Correct and clear definition: [A-Za-z].

If these characters are implied, they can be added explicitly:

[A-Za-z[\\\]^_`]

I suggest adding at least a new warning MIX_OF_LOWER_AND_UPPER_CHAR_CASE_IN_RANGE. It's especially actual if use the caseInsensitivity option. Or name it as RANGE_PROBABLY_CONTAINS_NOT_IMPLIED_CHARACTERS.

@parrt what do you think?