<details> and hard-coding of display:block

During the CSS WG face-to-face 2 weeks ago about <details> styling, you
mentioned something being hard-coded as display:block (and I didn't
immediately recognize what you were talking about).  After looking into
this, I'm guessing what you were referring to was the style attribute
inside of the shadow tree specified in HTML's rendering section
<https://html.spec.whatwg.org/multipage/rendering.html#the-details-and-summary-elements>
.

I think the solution for this is just to say that if we expose these parts
of the shadow tree as pseudo-elements, we need to change how that bit of
style is specified so that it's in the UA sheet instead of in a style
attribute.  I added this to my proposal (see last paragraph of the Proposal
#2 section
<https://github.com/dbaron/details-styling#proposal-2-pseudo-elements-new-ones-or-part>
).

Is that what you were talking about as something being hardcoded to
display:block, and does that conclusion make sense to you?

-David