I think this point in the SC is already addressed by 2.4.11 Focus Appearance (Minimum).

I don't think that's the case, the 2.4.11 is:

Unobscured: The item with focus is not entirely hidden by author-created content.

(Emphasis added).

2.4.11 requires it is not entirely hidden, the 2.4.12 one is that it cannot be hidden at all, i.e. no overlap from headers/footers at all.

Surely that is similar to meeting a level of contrast at AA, and a higher level at AAA?

Ah, thanks for clarifying the emphasis here. Sometimes you look at these things and you just don’t see it. Maybe it would be clearer to say:

In 2.4.11: Not fully obscured
In 2.4.12: Not obscured

to make the difference more glanceable.

It think we need to define what “not entirely hidden” means. Is 1px OK, a 5pixel area? If I put focus outline around the focused item and then “obscure the item with focus” using a pseudo :before or :after element, do I still meet the SC? (I personally find that “not obscured at all” is a reasonable criteria for a AA criterion 😉)

Yea, it's tricky, worth having a look over where it came from:

• Sticky headers/footers violation of SC 2.4.7? #952 about sticky footers/headers and 2.4.7.
• Add Obscure to 2.4.11 Focus Visible (Enhanced) #1145 for adding this bullet on obscurement.
• Focus Appearance (Minimum) SC2.4.11 - the Obscured bullet allows components to be completely obscured! #1271 about whether it turns into an exception.

We considered adding a measure for the obscurement, but it turns into another maths problem. It seemed better overall to indicate that it was not a good thing at AA, and have the AAA be the without-compromise version.

So for the clarification, do you mean something like this?

Not fully obscured: The item with focus is not entirely hidden by author-created content.

So for the clarification, do you mean something like this?

Not fully obscured: The item with focus is not entirely hidden by author-created content.

Yes, just to make the difference more glanceable.

I wonder if we – to keep the maths the same – could say “not less than the focus indication area is obscured”, which would come to this:

Not fully obscured: The item with focus has a visible area that is at least as big as the focus indication area.

Not fully obscured: The item with focus has a visible area that is at least as big as the focus indication area.

The focus indicator itself also needs to be "not fully obscured" for it to be obvious that focus has moved to that item. Perhaps something like this:

Not fully obscured: The item with focus has a visible focus indicator area equal to or greater than 1/4 of the focus indication area.

@juleskuehn we already have metrics for the focus indicator, the reason for this bullet is to add something for overlapping content.

This appears circular to me, as the focus-indication area is defined as what is visible:

The item with focus has a visible focus indicator area equal to or greater than 1/4 of the focus indication area.

Bullets 1-3 are about the focus indicator of the element, then bullet 4 is about whether the whole element is obscured.

Unless someone can point out a very simple metric, it seems best to have a general 'not fully obscured', and 'not obscured' as Eric suggested.

I've created a branch & PR for that, #1322

Sorry if that was less-than-clear. What I am trying to address is why Focus Appearance (Enhanced) mentions the focus indicator not being obscured at all:

No part of the focus indicator is hidden by author-created content.

But Focus Appearance (Minimum) does not mention the focus indicator being obscured, but rather the focused item being obscured:

The item with focus is not entirely hidden by author-created content.

For Focus Appearance (Minimum) it would be better, and more consistent, to state:

The focus indicator is not entirely hidden by author-created content.

The focus appearance (min) was discussed a lot, and what we wanted to avoid was creating an exception where the part of the focus indicator could be consistently hidden. Moving the target of the text to the element meant it was not un-doing the previous bullets.

The enhanced version (not discussed quite as much) was intended to be a higher-bar, no-compromise version so says that the indicator can't be hidden at all. I don't think there would be a problem aligning it to focus on the element, but it would be an issue the other way around.