[csswg-drafts] [css-line-grid] simplification to line-grid level 1

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== [css-line-grid] simplification to line-grid level 1 ==
One of the major source of complexity of the line grid is that in some
 cases, it can make the position depend on the size AND the size 
depend on the position, or (equivalently?) that it can make the 
intrinsic size depend on the position.

For example, if you create the grid on a vertical flexbox, and snap to
 the grid in the flex items, you're in trouble. Because of flexbox, 
the position of the various items depends on their size. But because 
of the line grid snapping, their size depends on their position.

Not all use cases for line grid depend on this problem being solved, 
but there are a number of use cases that do. For instance, using 
line-grid and grid together is desirable, and runs into the same 
issues. So we should solve it. At the same time, this is currently a 
large gap in the spec, and a big chunk of complexity that implementors
 are not enthusiastic about tackling immediately. So it would be good 
if we could solve that part later.

Here is a proposal to simplify line-grid for level 1 in a way which 
postpones this problem, while being completely compatible with the 
current definition so that we can reintroduce it in level 2 when we're
 ready to tackle the complexity.

1. add an `auto` value to the line-grid property, and make it the 
initial value. It does the same as match-parent on all elements, 
except elements that establish a BFCs where it would instead do the 
same as create

2. In level 1, remove the explicit `match-parent` value (but keep the 
behavior, since it is invoke by auto on most elements).

3. In level 2, bring back `match-parent`, and define how to resolve 
the cases where that makes size and position interdependent.

As far as I can tell, this is enough make sure that you never have 
situations (in level 1) where the size depends on the position AND the
 position depends on the size.

The simplification comes from part 2 but we need part 1 to keep the 
line-grid usable without the explicit `match-parent` value.


Side point: Even if an implementer was willing to bite the bullet and 
solve the interdependency problem now, I think the addition of the 
`auto` value would still be useful. In many cases it will create the 
grid on the right element without the author having to use the 
`line-grid` property manually, making it possible to merely use the 
line grid with the `line-snap` property without having to bother 
defining it.

Please view or discuss this issue at 
https://github.com/w3c/csswg-drafts/issues/880 using your GitHub 

Received on Tuesday, 10 January 2017 23:02:41 UTC