[css-flexbox] multiple lines when calculating container's max-content main size?

[davidsgrogan]

https://drafts.csswg.org/css-flexbox/#intrinsic-main-sizes says, emphasis mine:

2. Place all flex items into lines of infinite length.
3. Within each line, find the largest max-content flex fraction among all the flex items...
4. The flex container’s max-content size is the largest sum of the afore-calculated sizes of all items within a single line.

Question: if the lines are of infinite length, how could there be more than one line?

[astearns]

My first thought was that it might be due to an interaction with break-before or break-after in multi-line flex containers. But “The exact layout of a fragmented flex container is not defined in this level of Flexible Box Layout” so it may be more of a future thing and only in paginated contexts.

This pen shows Firefox honoring break-before: page in a non-paginated context, which I am not sure it is supposed to be doing: https://codepen.io/astearns/pen/QWMEBdY

[Loirooriol]

Firefox honoring break-before: page in a non-paginated context, which I am not sure it is supposed to be doing

My understanding is that an old version of the spec seemed to say this should happen, but that's no longer the case.

However, there is wrap-before/after: flex:

Force a flex line break immediately before/after the box if the box is a flex item in a multi-line flex container.

[astearns]

Ah, thanks! It looks like that’s not implemented anywhere, but it would be the reason for that step.

https://codepen.io/astearns/pen/JjyRXZg

[davidsgrogan]

Ah, great. Thanks for the info. Closing this issue now.