Was just thinking about the question of margins on inline boxes, particularly negative margins, and there's a bit of a problem with how it's defined to work atm:

Consider an inline element with a negative margin:

 <span style="margin-block: -0.1em">set tight</span>

If we introduce another element, this prevents the margin from acting as expected:

 <span style="margin-block: -0.1em">set <em>tight</em></span>

Generally we try to make sure adding unstyled inline elements has no effect on layout, so we need to do something to fix this, maybe propagating the negative margin to descendants somehow?