[Webkit-unassigned] [Bug 176384] Fixed-position block within fixed-position, overflow-scrolling block is unexpectedly clipped

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=176384

--- Comment #1 from Evan Chaney <evan at artefactgroup.com> ---
Although nested-fixed-position blocks are a somewhat odd construction as best I can tell this case does appear to be a valid construction/expectation.

The CSS 2.1 spec. establishes blocks in normal flow with overflow other than “visible” establish a new formatting context:

https://www.w3.org/TR/CSS2/visuren.html#normal-flow

However, “CSS Positioned Layout Module Level 3” establishes absolutely-positioned blocks are removed from normal flow:

https://www.w3.org/TR/2016/WD-css-position-3-20160517/#pos-sch

It also establishes fixed-positioned blocks are included when the spec. references absolutely-positioned elements:

https://www.w3.org/TR/2016/WD-css-position-3-20160517/#abs-pos

Given these rules it seems a fixed-position block should not be subject to the formatting rules of a containing parent.

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