[css-position-3] Define what out of flow means

[fantasai]

https://www.w3.org/mid/121317FE-7226-4FD0-A6F5-C2419BEBD904@rivoal.net

[frivoal]

So far, this is a defined term in css-display: https://drafts.csswg.org/css-display-3/

[Loirooriol]

Seems to me that some terms defined in CSS Display could be moved to CSS Position:

• https://drafts.csswg.org/css-display-3/#containing-block
• https://drafts.csswg.org/css-display-3/#containing-block-chain
• https://drafts.csswg.org/css-display-3/#initial-containing-block
• https://drafts.csswg.org/css-display-3/#out-of-flow
• https://drafts.csswg.org/css-display-3/#in-flow

Though less sure about in-flow/out-of-flow since float is also involved.

[fantasai]

@Loirooriol containing block is a pretty fundamental concept to layout: if we removed positioning entirely from CSS, it would still be needed. So I think the fundamental definition belongs in Display. Position just has the most complicated set of rules, and it crosses through various layout modes, so it's got more text about it than other layout models. So Display should have a cross-reference to css-position, but css-position shouldn't be defining the term.