[css-scroll-snap-1] Why does scroll-snap-align: both snap in each axis independently?

[flackr]

In the css-scroll-snap-1 spec section 4.1.1 it states that for the scroll-snap-axis both:

The scroll container snaps to snap positions in both of its axes independently (potentially snapping to different elements in each axis).

What's the use case for this? I would expect the common case is that the author would expects the UA to snap to both axes of that element if it snaps to that element. If an author wants to snap independently on different axes (e.g. for rows and columns of a table) they can specify snap alignment in a single axis.

Use cases where you'd for sure want alignment in both axes are any sort of 2d selection UI, e.g. a 2d panning map with multiple POI that snaps to a particular POI.

This in particular makes using the snapchanged / snapchanging apis in css-scroll-snap-2 more complicated if you do want to know which element is aligned in both axes.

[flackr]

In fact, the description of the axis values even says that it affects "whether snap positions are evaluated independently per axis, or together as a 2D point." Is it not expected that both should be treated as a 2D point or was the intention to add another value for evaluating it as a 2d point?

[fantasai]

Some prior discussion on this:

• https://drafts.csswg.org/css-scroll-snap/issues-by-issue#issue-67
• https://www.w3.org/TR/2016/WD-css-scroll-snap-1-20160623/#scroll-snap-type