"visible" has ambiguous language on scrolling

[WilcoFiers]

The definition of "visible" is based on pixels changing when something is made transparent. That works fairly well, but it doesn't account for things that are not in the viewport, but could be scrolled into view in some way or another.

A common sense understanding of that is if something isn't in the viewport, some attempt needs to be made to scroll it into the viewport. That's something that can definitely be added to the definition, and should be. But that still leaves a bit of a gap. That's user agent scrolling. What about scrolling behaviour implemented using content scripts? That includes basic things like a custom scrollbar, but also stuff like navigation in Google maps and the like.

[Jym77]

The definition of "visible" is based on pixels changing when something is made transparent. That works fairly well, but it doesn't account for things that are not in the viewport, but could be scrolled into view in some way or another.

I don't understand. Our definition of "visible" is (emphasise mine):

Content is considered visible if making it fully transparent would result in a difference in the pixels rendered for any part of the document that is currently within the viewport or can be brought into the viewport via scrolling.

Maybe we need to better define what we call "scrolling" if this includes several different operations.

[WilcoFiers]

Fair point, yeah it isn't too clear what "via scrolling" means here.

[Jym77]

https://drafts.csswg.org/cssom-view/#scrolling-area may help.
But I do have a hard time convincing me that it means what we need 🤯

[carlosapaduarte]

New URL for scrolling area: https://www.w3.org/TR/cssom-view-1/#scrolling-area