Interactive test on 'background-attachment': 'local' versus 'scroll' values
Current background-attachment value: local
VeryLongWordHereToTriggerAnHorizontalScrollbar 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.