BASIC uses the full ASCII character set.  This set includes:

   o  The letters A through Z (upper- and lowercase)
   o  The numbers 0 through 9
   o  Special characters

  The compiler:

   o  Interprets lowercase letters as the  corresponding  uppercase  letters
      unless they are part of a string constant
   o  Does not process nonprinting characters unless  they  are  part  of  a
      string constant
   o  Does not process characters in REM statements or comment fields

  In string constants, lowercase letters remain  lowercase  and  nonprinting
  characters are allowed.