ENDLOOP;

  The initial POSITION is required to ensure that the whole of the
  filter_buffer is processed, because the editing point is undefined
  at the start of each filter. Then, as each number is processed, the
  editing point is moved to the end of the number. The MOVE_HORIZONTAL
  procedure call is necessary because the previous POSITION leaves the
  editing point at the last character of the number, which would
  result in an immediate match on the next call to SEARCH_QUIETLY.