[cssom-view] "root element" is undefined

[cvrebert]

This specification uses the term "root element" approximately 25 times. For example:

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https://drafts.csswg.org/cssom-view/#scrolling
(4) Perform a scroll of viewport to position, and document’s root element as the associated element, [...]

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https://drafts.csswg.org/cssom-view/#extensions-to-the-htmlelement-interface
(1) If any of the following holds true return null and terminate this algorithm:
[...]

• The element is the root element.

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However, none of the instances of the term "root element" are hyperlinked, nor is an explicit definition given elsewhere in the spec.
See also #7786