[css-anchor-position] position-visibility initial value should be `always`, not `anchors-visible` ?

[chrisdavidmills]

When writing MDN docs for anchor positioning, I was a bit confused by position-visibility — the spec says "initial value" is anchors-visible, but surely it should be always?

From testing:

• If you don't set a position-visibility value, an anchor-positioned element is always visible provided it is inside the viewport, regardless of the visibility of its anchor. This is the behavior always gives as well.
• anchors-visible, on the other hand, causes an anchor-positioned element to be hidden if its anchor is not visible at all in the viewport.

My demo illustrates the behavior of the currently-supported values, in case that is helpful.

[tabatkins]

The current impl in Chrome isn't reflecting the spec; it indeed is using "always" as the initial value. But the spec's text is intentional - if your anchor is off-screen or otherwise scrolled off, you usually want it to hide.

[chrisdavidmills]

The current impl in Chrome isn't reflecting the spec; it indeed is using "always" as the initial value. But the spec's text is intentional - if your anchor is off-screen or otherwise scrolled off, you usually want it to hide.

Thanks @tabatkins, that makes sense. So as soon as an element becomes an anchor-positioned element, per spec it should adopt the anchors-visible behavior?

The way we've currently written it reflects the current implementation, so I think it is OK to publish it like that for now. We'll just have to change it once behavior updates.