[css3-background][css-writing-modes] background-position:bottom to root elements

Gérard and I are a little in trouble understanding expected behavior, appreciate advices.

First question is hopefully easy; see this test file[1]. I suppose, in all browsers, you’ll see a cat NOT touching the bottom of the window. Is this the expected behavior? I read “The Canvas Background and the Root Element”[2], and it reads to me that this is correct, but experts’ confirmation appreciated.

The second question is when "writing-mode: vertical-rl" is applied to this document.

My understanding is, given the definition above, “background-position: right” touches the right edge of the window, while “left” does not. And if “writing-mode: vertical-lr”, “left” touches the left edge, while “right” does not.

Am I reading the Background spec correctly?

[1] http://jsbin.com/vuzajo/1/edit?html,css,output
[2] http://dev.w3.org/csswg/css-backgrounds-3/#root-background

/koji