[css3-backgrounds] Example XV inconsistent with prose of section 3.6

      http://dev.w3.org/csswg/css3-background/
      3.6  The 'background-position' property
      If only one value is specified, the second value is assumed to be 'center'.

      3.10  The 'background' shorthand property
          p { background: 40% url("chess.png") / 10em gray

                 round fixed border-box; }

      is equivalent to:
      ...

          background-position: 40% 50%;
      ...


I believe this is incorrect.

The equivalent is
        background-position: 40% center;
or
        background-position: 40%;


Am I misunderstanding?