The character set specified by the Fortran 95 and Fortran 90
  Standards consists of all uppercase and lowercase letters (A-Z and
  a-z), the digits 0-9, the underscore (_), and the following special
  characters:

          (blank or space)       :    (colon)
     +    (plus sign)            "    (quotation mark)
     -    (minus sign)           %    (percent sign)
     *    (asterisk)             &    (ampersand)
     /    (slash)                ;    (semicolon)
     (    (left parenthesis)     <    (less than)
     )    (right parenthesis)    >    (greater than)
     ,    (comma)                ?    (question mark)
     .    (period)               $    (dollar sign)
     '    (apostrophe)