Why the exclamation point in another StackOverflow posting involving telephone number REGEX?
regex
Solution
You're absolutely right, the `x` is sufficient. `!` just matches a literal `!`, inside a character class or out. The only place it has any special meaning is when it's part of negative lookahead or a negative lookbehind.
Problem
In A comprehensive regex for phone number validation, the accepted answer has a number of comments. One of the comments, by @jcmcbeth, suggests the following simple regular expression to use to obtain the digits of the telephone number submitted by a user: ``` string.replace("[^\d+!x]", "") ``` Immediately following the comment with this suggested regular expression, another questioner asks `why the !x part?`, which is then answered in the next comment: `The !x is there to keep any "x" character from getting stripped`. This makes sense to me, except for the exclamation point `!`. Looking at documentation for character classes in regular expressions, I do not see that the exclamation point is a special character, and it doesn't seem to me that the `x` requires a special character preceding it. Also, from the discussion in the linked question, I do not see any comment indicating that an exclamation point might be part of a telephone number (which would explain its inclusion in the negated character class). Can someone please explain to me why the exclamation point is present? Thanks.