I want to validate that the characters are alpha numeric:
Regex aNum = Regex(\"[a-z][A-Z][0-9]\");
I want to add the option that there migh
[A-Za-z0-9\s]{1,} should work for you. It matches any string which contains alphanumeric or whitespace characters and is at least one char long. If you accept underscores, too you shorten it to [\w\s]{1,}.
You should add ^ and $ to verify the whole string matches and not only a part of the string:
^[A-Za-z0-9\s]{1,}$ or ^[\w\s]{1,}$.