In https://wicg.github.io/spatial-navigation, I've found myself wanting to refer to a scroll-able thing that isn't already scrolled to the maximum. (and in my case, I only cared about manually scrollable things, not things that can be scolled only by script, like overflow:hidden)

For now, I've rolled my own definition (see below), but this should be in a css spec somewhere. Maybe this is CSSOM-View. Maybe there should be a new CSS spec that deals with the general processing model for scrolling, to which various bits of CSSOM-View and CSS-scrollsnap could refer to (and/or be moved to).

An element e can be manually scrolled in a given direction d if:

• The principal box established by e is a scroll container, and
• if d is up or down, the computed value of the 'overflow-y' property is not ''overflow/hidden'', and
• if d is left or right, the computed value of the 'overflow-x' property is not ''overflow/hidden'', and
• e is not at the scroll boundary in the direction d
• e is not snapped to the last ''mandatory'' snap point in direction d