[resize-observer] "Calculate depth for node" is unclear

[smaug----]

https://drafts.csswg.org/resize-observer/#calculate-depth-for-node-h doesn't explain what
parent-traversal path means. Does it include Shadow DOM? In which way? Is ShadowRoot included?

[emilio]

FWIW in Chromium it doesn't seem to include shadow DOM. But that may be an oversight?

https://cs.chromium.org/chromium/src/third_party/blink/renderer/core/resize_observer/resize_observation.cc?l=32&rcl=22be1c05550aaa7f597f0cee5174500fd36588da

cc @atotic

[gregwhitworth]

Hmmm, that's a good question. I can't think of why shadow DOM shouldn't be included. I think it makes sense only if the shadow DOM has a mode of open though. @smaug---- @atotic @tabatkins any thoughts?

[emilio]

Why only open shadow trees? That doesn't make much sense to me. We should probably either use the flat tree depth, or the depth using "either parentNode or host if I'm a shadow root" (not sure the spec concept for that).

[atotic]

We should specify how to calculate depth with Shadow DOM. Would replacing

Let p be the parent-traversal path from node to a root Element of this element’s DOM tree.

with

Let p be the parent-traversal path from node to a root Element of this element’s flattened DOM tree.

work?

[BorisChiou]

Let p be the parent-traversal path from node to a root Element of this element’s flattened DOM tree.

This looks ok to me. Actually, Firefox uses this way (I.e. calculates the depth by traversing the element’s flattened DOM tree) right now.

[smaug----]

'parent-traversal path' isn't defined.