.*\.(com|org|edu|us|cn|ca|de|mus|gov)

  another common case:
     (a|b|c|...|z)(0|1|2|...|9)(a|e|i|o|u)

  When your "or"s all just are a single char,
  you can use the character-set notation:

   the pattern
     [abcdef...z][0123456789][aeiouAEIOU]
   matches
     "a4e"
     "z9A"
   but not
     "ab01A"
- square-brackets are character-sets:
   they match EXACTLY ONE character.

  Within square-brackets, "-" can be used
  for a range of characters:
    [a-z][0-9][aeiouAEIOU]
  is a pattern equivalent to above.
  
  Note:  "any roman letter upper or lower case"
    is [a-zA-Z]   --  NOT    [A-z]
   [A-z] includes other letters between
    'Z' and 'a' -- as per an ascii chart

- finally: some character-sets are so common,
  they have additonal shortcuts:

      [A-Za-z]  is also [[:alpha:]]
        is also \w is also  \p{L}