[css-lists] List marker position with anonymous first_child which dose not have text.

[cathiechen]

Fixing issue 715288 in blink recently, and I think it might be better to discuss it here.
Case: https://wptest.center/#/4apjp4
The marker position of four browsers are different.
Do we need a consistency here?
@kojiishi @FremyCompany @upsuper @phistuck

[upsuper]

I guess there are two questions:

1. in which case there should be an empty line before the image, and
2. whether the marker should be aligned to the first baseline

For the first question, it seems Gecko puts an empty line when there is an inline element, while Blink and WebKit do so when there is no inline element, and Edge does so in both cases. However, I would argue that there probably shouldn't be an empty line in either case, just like when we set display: block on <li>s. So this is probably a bug for every browser here.

If we ignore the difference from the first question, it seems WebKit and Gecko agree on that the marker should be aligned to the first baseline while Blink kinda aligns it to the top. (Since Edge has an empty line for both, it is hard to say what's the real behavior underlying.)

Maybe we would allow using CSS Box Alignment properties to control where ::marker should be positioned on day... but for now probably using first baseline may make more sense? I don't know.

[upsuper]

For the second question above, CSS 2.2 says:

CSS 2.2 does not specify the precise location of the marker box

so it's explicitly undefined, and it seems CSS Lists 3 doesn't make it clear either, so I guess it's probably also fine that we continue leaving the second question undefined for now...

[cathiechen]

@upsuper I'm agree with you.
Btw: Blink has gotten rid of the leading empty line. It works in chrome canary.