I’m investigating an interop issue with grid/flex layout for <fieldset>. As you can see from the table below the grid/flex layout support of <fieldset> varies a lot between browsers. Only Firefox and IE 11 handle <fieldset> with display: flex.

Test case: http://codepen.io/anon/pen/MaYBoX
or a shorter version:

<fieldset style="display: flex">
    <legend>Legend</legend>
    <div>These fields</div>
    <div> shouldn't be</div>
    <div>stacked vertically</div>
</fieldset>

It’s interesting that Edge removed <fieldset>’s flex layout support that was supported in IE11. May be someone from Microsoft can share some insights about this decision.

According to http://www.w3.org/TR/CSS21/visuren.html#display-prop the display property “Applies to: all elements”.

Can we decide whether 'display' property should have rendering effect on <fieldset>.