php only allow letters, numbers, spaces and specific symbols using pregmatch
If you not only want to allow ASCII, then use Unicode properties:
preg_match('/^[\p{L}\p{N} .-]+$/', $firstname)\p{L} is any letter in any language, matches also Chinese, Hebrew, Arabic, ... characters.
\p{N} any kind of numeric character (means also e.g. roman numerals)
if you want to limit to digits, then use \p{Nd}
The only difficult bit here is the dash.
For spaces and dots, you can simply add them to your character class, like so:
'/^[a-zA-Z0-9 .]+$/'Easy.
The dash is slightly harder because hyphens have special meaning in a character class like this (as you already know, they're used for ranges of characters like a-z). In order to specify a hyphen in a character class, it must be the first character in the class (ie it must not be between two characters, otherwise it is treated as a character range marker).
So your expression would be:
'/^[-a-zA-Z0-9 .]+$/'Hope that helps.