[Scott MacVicar]

Yeah it will work, it allow characters for a-z A-Z underscore and numbers in the range 0-9.

Hence the

a-zA-Z_0-9

but i believe that

PHP Code:

if (!preg_match("/^\w+$/", $username)) {
  eval("standarderror(\"Invalid Characters you can only use a-z, 1-9 or an underscore in your username.\");");
  exit;
} 


as \w represents word in perl thought it depends on locale settings