[css-anchor-position] When to invalidate "last remembered position-try option"?

[tabatkins]

Currently, we're just using essentially the same conditions for forgetting "last remembered position-try option" as we do with "last remembered size".

But the chosen position-try option depends on more stuff than the size. Notably, what happens if you change the 'position-try-options' list? And what happens if the @position-try rules are changed? (mutated, or deleted, or we add a new one that was already referred to while not previously existing)

And theoretically, other things can change the styles, like, what if the element with a referenced anchor-name changes?

Weighing both usability with difficulty, I propose:

• We forget the remembered option if the computed value of 'position-try-options' changes
• We forget the remembered option if any of the referenced @position-try rules are added/removed/mutated.
• That's it. (If other things that affect the style change, but they still don't result in having a non-overflowing position, oh well.)

[css-meeting-bot]

The CSS Working Group just discussed [css-anchor-position] When to invalidate "last remembered position-try option"?, and agreed to the following:

• RESOLVED: forget if position-try CSS changes or any of the try blocks change

The full IRC log of that discussion

<chrishtr> TabAtkins: there is a "last remembered position" try option if you previously did something and now the try blocks fail, to allow users not to see something jump around.
<chrishtr> TabAtkins: but what if there are various kinds of changes that more explicitly invalidate those try blocks that previously appliied?
<chrishtr> TabAtkins: in service of a simple rule, consistency and ease of implementation, we should remove the previously remembered size if try blocks are added, removed or mutated, or properties that specify the try blocks changed
<chrishtr> TabAtkins: proposed resolution: forget if position-try CSS changes or any of the try blocks change
<chrishtr> RESOLVED: forget if position-try CSS changes or any of the try blocks change
<fantasai> +1