Martin and I had a discussion on IRC last night (after this email was sent) and we finally reached a consensus on the correct behavior. Marc (uwog) and Tomas also seem to agree with this, so let's go and actually implement it:
"If a run is not transparent, draw the color/image into the background rectangle. If a run is transparent, it should ask its parent container to draw into the given background rectangle, until the parent isn't transparent or the parent == the document." For the case of background images, I suggest we investigate Tomas' suggestion, which is basically what Martin and I had discussed the previous evening. It would follow the same semantics as the above, but hopefully would optimize so as to blit only the required RGBA bits onto the screen. Dom
