[css-align] inconsistency for fallback behavior for space-{around,evenly}

[cbiesinger]

https://drafts.csswg.org/css-align/#valdef-align-content-space-around

This section specifies a fallback alignment of 'safe center'

https://drafts.csswg.org/css-align/#overflow-values

This says that an unspecified value for overflow-position has certain behavior that is closer to unsafe and also says UAs that have not implemented the “smart” default behavior must behave as [unsafe](https://drafts.csswg.org/css-align/#valdef-overflow-position-unsafe).

Those seem at odds with each other?

[cbiesinger]

I'll also note that safe is incompatible with the css-flex definition of space-around: https://drafts.csswg.org/css-flexbox/#valdef-justify-content-space-around

[Psychpsyo]

Those seem at odds with each other?

From how I read it, the two css-align sections don't contradict each other.

The moment something like space-around falls back to safe center, it has an <overflow-position> of safe and therefore behaves as safe.
Whether or not a user agent supports the smart default behavior has no bearing on what happens since the default behavior isn't even applied.
(Well, it is applied while the fallback alignment is not used but in that case it doesn't do anything since space-{around,evenly} never overflow. The moment they would overflow, they fall back to safe center)

[cbiesinger]

I see, but that reading still leaves the issue with the css-flex compatibility.

[Psychpsyo]

I also think it's worth noting that at least Chrome and Firefox currently implement the css-flex fallback to center, not the css-align safe center one. (not sure about Safari)
But I think safe center would make more sense and copying the safeness of the original alignment would be ideal, at least for space-around and space-evenly. (Since something like unsafe space-around currently falls back to safe center, meaning that it does the opposite of the specified safeness)

[Loirooriol]

css-align changed in #5088, I guess @fantasai forgot to change css-flexbox.

[tabatkins]

Well, flexbox's older definition of the properties doesntt have a way to specify safe/unsafe. It defaults to unsafe behavior in general.

We really need to finally just remove the property definitions from flexbox; they persist solely for Process reasons, since Flexbox is still a more mature spec than Align, technically (CR vs WD). But we are allowed to reference specs one level less mature; relying on Align would just prevent Flexbox from going to Rec until Align went to CR (which I'm fine with).

---

Anyway, Chrome has matched the Align behavior now (safe centering as the fallback), so it looks like the issue is just that Flexbox is saying wrong things.

[aethanyc]

@fantasai After #10154 and the edits in b6c01a4, is there anything left to do here?

[fantasai]

@aethanyc Yes, I think you're right. Closing.