Section 6,6: Nonprintable_Characters

 The form-feed character (0C hex) is treated as a blank without
 causing a diagnostic message to be issued.  In addition, a source
 record of length 1 containing a form-feed character causes the
 compilation source listing to begin a new page.

 A source record of length 1 containing a Ctrl-Z character (1A hex)
 is treated as a blank line.  Such a record is created by the
 ENDFILE statement, if the command line option -vms is specified.

 All other control characters are valid, except 00(hex) and 01(hex).

 If you must use a nonprintable character in a character constant,
 use the CHAR intrinsic function, in conjunction with the
 concatenation operator if necessary.  For example:

    CHARACTER*(*) ESC_BRACKET
    PARAMETER (ESC_BRACKET = CHAR(27)//'[')