[css-grid-3] Masonry - align-tracks / justify-tracks not defined sufficiently - has issues with spanning items

[bfgeek]

Unclear is align-tracks / justify-tracks is a good design see previous issue:
#8207

However currently underspecified. Specifically:

1. Unclear how to deal with items which are spanning multiple tracks. I played very quickly with this in Firefox and unclear what was occuring.
2. "stretch" needs to be defined precisely. Specifically you can get into an over-constrained situation with items having max-height specified on them. How to you distribute the excess space when one item hits its max?
3. From talking with web-developers the fact that flexbox flexes based on the content box was confusing, and likely shouldn't be carried forward to other modes. Grid doesn't do this - we shouldn't do this for masonry as well.
4. Increasing auto-margins isn't how flexbox works, should likely rely on flexbox behaviour here?

Edit - a simple example of the spanning issue: https://www.software.hixie.ch/utilities/js/live-dom-viewer/?saved=11095

[lukewarlow]

These features are being dropped #8207 (comment)

[nt1m]

I'll close this issue since the feature was removed.