[css3-background] background-attachment: local

We were looking implementing 'background-attachment: local' in Gecko, and
ran across the following problem in its definition:

The goal of 'background-attachment: local' is to allow authors to get
the behavior of 'background-attachment: scroll' on the canvas background
when setting the background of an element with 'overflow: scroll'. IMHO
this should have been the behavior of 'background-attachment: scroll'
in the first place, but the WG at the time decided it should behave like
'fixed' on such elements; therefore we added a new keyword, 'local', in
level 3.

The spec defines this for the background's "attachment", but it doesn't
for its positioning. Case to consider: a background image positioned to
the bottom right corner. In the case of 'background-attachment: scroll'
on the canvas, it is at the bottom of the scrollable area, not the bottom
of the viewport. Similarly, 'background-attachment: local' should put
such an image at the bottom of the scrollable area, not the bottom of
the viewport. However, the spec doesn't specify this, so would need to
be amended to fix that.

Thoughts?

~fantasai

Received on Wednesday, 22 May 2013 04:27:48 UTC