In Implicit Anchor Elements it says

...
The implicit anchor element of a pseudo-element is its originating element, unless otherwise specified.

Finding an Anchor then says

1. If anchor spec was not passed, return the default anchor element if it exists, otherwise return nothing.

2. If anchor spec is auto:

   1. If the Popover API defines an implicit anchor element for query el which is an acceptable anchor element for query el, return that element.
   2. Otherwise, return nothing.

   ...

It seems that given a pseudo element this would return its originating element in step 1 if the default anchor was auto (i.e position-anchor: auto and no anchor spec).

However, if the anchor spec is auto (step 2), then it only returns an implicit anchor for a Popover API and not for pseudo elements, so it would return nothing.

It wasn't clear to me if this is intentional or an oversight.

@tabatkins @fantasai