9.2.5 in 26300 as corrected and amended so far

[MURATA Makoto]

Dear colleagues,

Another reviewer of the JIS ODF 1.1 draft asked why
an ellipse rather than a circle in the para (shown below)
in "Concave" in 9.2.5.

  The draw:concave attribute specifies whether the
  polygon is convex or concave. For a convex polygon,
  the polygon corners are located on a single ellipse
  which has its center in the center of the polygon.
  In a concave polygon, two such ellipses are required,
  and corners that are located next to each other are
  located on different ellipses. An example for a convex
  polygon is a hexagon. An example for a concave
  polygon is a star. For concave polygons, an additional
  draw:sharpness attribute is required.

I'm afraid that I do not understand this paragraph well.
Please enlighten me.

Regards,
Makoto