The FIND_NONMEMBER function locates the  first  character  in  a
  string  that  is  not a member of a specified set and returns an
  integer value indicating the position of the  character  in  the
  string;  the  function returns 0 if the characters in the string
  were all members of the set.

  Syntax:

     FIND_NONMEMBER( string, char-set )

  The 'string' parameter is a string value, and the 'char-set'  is
  a value of type SET OF CHAR.