Re: [CSS21] 17.5.2.1 Fixed table layout and percentages

Yet another issue:

Widths are taken from cells of the first row. Is that first in source 
order or in display order?

According to 17.2, a `display: table-header-group` is *displayed* before 
any other row or row group. If however it is after a row or row group in 
source order, both orders may not be the same.

(This may be illegal HTML with <thead>, but can also happen with table-* 
CSS display on non-table elements.)

Regards,
-- 
Simon Sapin