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However, a nested :is() can not bypass the limitations imposed by
an outer pseudo. So for example, since :host() only allows a
compound selector list, an :is() pseudo inside a :host() can also
only accept a compound selector list.

Bug: 568705
Change-Id: I879c83172386b8732f0c3e3c540c74e8d3eb0ecb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2438387
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813594}