The regex validation in RSForm! Pro uses the PHP preg_match() function.
If your regex pattern does not work, please remember that the PCRE implementation requires delimiters. A delimiter can be any non-alphanumeric, non-backslash, non-whitespace character. Often used delimiters are / and #.
For example, the following:
will work and will match any number in a string. However, the following will not work: ([0-9]) since it is missing the mandatory delimiters.
You may add pattern modifiers at the end of the pattern. One of the most used modifiers is i. It will match the pattern regardless of character case (lowercase, uppercase or a combination of the two) used:
The above pattern will match any letter, be it uppercase or lowercase thanks to the i modifier.