19.231 draw:z-index, add this:
The draw:z-index values increase from back to front.
For a shape on which the attribute style:run-through (20.343) with value foreground is in effect, producers should not generate a draw:z-index value that is smaller than the value of any draw:z-index on a shape on which the attribute style:run-through with value background is in effect.
Producers SHALL NOT generate a draw:z-index for shapes that are children of a <draw:g> element (10.3.15) or a <dr3d:scene> element (10.5.2).
20.343 style:run-through, add this:
The default value for this attribute is foreground.