Define table height redistribution to row groups

[atotic]

How should table height be redistributed to table's row groups?

Current spec does not specify how should table's css height be distributed to row groups.

This is what the existing browsers do when row-group heights are auto:

Chrome 87: distibutes everything to 1st body
Safari 13.1: distributes everything to 1st body
Firefox 83: distributes evenly
Edge 17: distributes evenly
Upcoming Chrome TablesNG: distributes everything to all bodies evenly

Testcases:
https://jsbin.com/jetamas/1/edit?html,output
http://wpt.live/css/css-tables/height-distribution/computing-row-measure-0.html

It'd be nice for implementations to converge. I can see arguments for both:

1. distributing only to TBODY
   Pro: The author would like to fill some vertical space, but keep headers tight. This can also be accomplished by giving height to tbody.
   Con: No way to distribute heights evenly between THEAD/TFOOT and TBODY. Workaround: use multiple TBODY does not work in old Chrome.

2. distributing to all row groups
   Pro: simple to understand, can explicitly size THEAD if needed
   Con: additional CSS needed for "common case".

What solution is web compatible?

• FF does not handle explicit heights on THEAD well.

[bfgeek]

https://bugzilla.mozilla.org/show_bug.cgi?id=1806961 from developer expecting Blink/WebKit behaviour.