The FIND_MEMBER function locates the first character in a string
  that is 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 not
  members of the set.

  Syntax:

     FIND_MEMBER( string, char-set )

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