Inline nodes in our layout tree have a position, so let's show it. By
centralizing the logic for this, block nodes now lose their redundant
'content-size' dump info which is already part of the box model dump.
This is what the spec tells us to do:
The root element’s display type is always blockified,
and its principal box always establishes an independent
formatting context.
Additionally, a display of contents computes to block
on the root element.
Spec link: https://drafts.csswg.org/css-display/#rootFixes#1562
