I'm opening this on behalf of Christian Biesinger as he posted a question to www-style. Moving the thread here:

I learned today that not all browsers ignore percentage margins for
intrinsic width computations. In this testcase:
http://software.hixie.ch/utilities/js/live-dom-viewer/?%3C!DOCTYPE%20html%3E%0A%3Cstyle%3E%0A%20%20div%20%7B%20float%3A%20left%3B%20border%3A%20solid%3B%20%7D%0A%20%20p%20%7B%20margin%3A%2010%25%3B%20%7D%0A%3C%2Fstyle%3E%0A%0A%3Cdiv%3E%0A%20%20%3Cp%3Ethisisaword%3C%2Fp%3E%0A%3C%2Fdiv%3E

Chrome/IE 11/Edge overflow the box, whereas in Firefox they don't. I
actually have no idea how they implement this! I'm also unsure what the
spec requires...

-Christian

On Mon, Jul 25, 2016 at 5:24 PM, Christian Biesinger [email protected]
wrote:

Hello!

Question about https://drafts.csswg.org/css-flexbox/#intrinsic-main-sizes

This algorithm wants to use the outer flex base size. But in general, for
intrinsic sizing purposes, percentage margins get treated as zero. Should
that be used here as well?

Also, is there a reason why min-size is ignored for the purpose of this
algorithm?

thanks,
-Christian