I have the following function

public function alpha_custom($str)
{
   return ( ! preg_match("/^([-a-z0-9_-])+$/i", $str)) ? FALSE : TRUE;
}

So ,if the string contains anything other than alpha-numeric characters, underscores or dashes then it will return false.

Now i want to add the following

1. SPACE
2. &
3. ( AND )
4. . (period )

Please help me.
Thanks.