[css-display-3] Can the root float?

In https://github.com/w3c/csswg-drafts/pull/8095 we established that:

• the root establishes an independent formatting context
• the ICB establishes a block formatting context (thus an in-flow root is a block-level box)

This fully defines the root box’s layout.

However, we noted that some implementations don't handle float on the root element, so we have a question: should float apply to the root element? If not, is that a used value of none or do we compute it to none?

Current testing shows that Blink and Webkit can float the root, and Gecko can't. Also, among the print implementations some support float, some don't, and some don't have proper block layout on the root

Read the conclusions in PR 8095 first, then compare the linked live DOM and print-implementation examples for root elements with float set. Determine whether float applies to the root and whether any exception is computed or used-value behavior; done means the CSS Display specification has a resolved, interoperable rule.