[csswg-drafts] [css-containment] Clarify "must be" statements

frivoal has just created a new issue for 
https://github.com/w3c/csswg-drafts:

== [css-containment] Clarify "must be" statements ==
In a few of places, css-containment uses the phrasing "the element 
must be a <foo>",
where <foo> ∈ { **formatting context**, **stacking 
context**}.

First, this is ambiguous. While it is meant as a requirement that the 
UA changes the element into being a <foo> if it isn't one already, 
it could be read as implying the the effect under discussion does not 
apply if the element isn't already a <foo>.

Moreover, when the element isn't a &ls;foo>, it doesn't say how to 
make it into one. When <foo> is a **stacking context**, this is 
fine, as there no ambiguity how turn into one of these, but for 
**formatting context** it is a problem, as there's multiple ways an 
element could be become one, and the spec doesn't say so.

Please view or discuss this issue at 
https://github.com/w3c/csswg-drafts/issues/830 using your GitHub 
account

Received on Friday, 23 December 2016 12:15:01 UTC