Pos function

  DECLARATION:  Pos(SubString, S : String);

      PURPOSE:  Searches for a substring in a string

         UNIT:  System

  RESULT TYPE:  Byte

      REMARKS:  Pos searches S for the first occurrence of SubString and
                returns the integer value of the position of the first
                character of SubString within S. If no occurances
                are found then it returns 0.