Cpos (string, substring)
Cpos (string, substring, n)

   Synopsis:
      Returns the position in the string of the first occurence of any character
         from the substring

   Notes:
      (Axbasic labels the first character in the string as 1, the second as 2,
         and so on.)
      If none of the characters in the substring occur in the string, 0 is
         returned. If either the string or the substring are empty strings, 0 is
         returned.
      If the third argument is specified, the search begins at the nth character
         in the string and proceeds to the right. Cpos (string, substring, 1) is
         interchangeable with Cpos (string, substring).
      If n is not an integer, it is rounded off. An error occurs if n is zero
         or a negative number.
