Re: [css-box] shrink-to-fit and floats

Thank you, Tab.

> ​To make sure we're on the same page, here's the markup:

Yes, we agree on the markup, and the window size can be 500px.

I understand the preferred width, available width, minimum preferred width
formula used to compute shrink-to-fit width; I am only confused about how
we compute the width of the div, for the purposes of determining the
preferred
width of the section.

> ​If the div had "margin-right: -10px", all the above still applies, but
> the calculation of the minimum width that doesn't trigger overflow
> changes.  Overflow happens when the *margin box* of an element is
> wider than its container, and in this case the margin box is 0px wide
> - 10px from width, minus 10px from margin-right.

​Am I taking you correctly, then, that margins are treated differently
when determining shrink-to-fit and ordinary width, namely that ​right
margins are not ignored for computing shrink-to-fit width yet are
ignored for computing ordinary width (in situations where that's
applicable)?

​Every other part of the layout for this example you and I agree on.​

​I suppose I can reduce my confusion now to this question:
when is the margin-right ignored, and when is it not?

It sounds like margin-right is ignored during the layout of block-level,
non-replaced elements in flow, when computing their actual layout,
but it is not ignored when computing their width for the purposes of
determining the preferred [minimum] width of a container.

> Sizing spec does correct this lack and define things more precisely.

That's a useful draft to be aware of, thank you. I think the relevant
sentence of that specification would be this one, in §4.3:

> Otherwise, if the computed inline-size of the block is fit-content, auto,
> or fill, its min-content inline-size contribution is its min-content
> inline size plus any inline-axis margin, border, and padding.

Is this referring to the inline-axis (that is, the left & right) *used*
values
for margin, border, and padding or the *computed* values?

The used values are the ones computed by ignoring the specified
margin-right, while the computed values would be the expected ones.
It may be best to amend that draft to make the choice here clearer.

—Pavel Panchekha