Empirically, the root element’s box is laid out like a block-level box in a block formatting context. But I can’t find any information in the specs about anything creating the context into which the root element’s box would be laid out.

According to the definition of formatting context in the Glossary, formatting contexts are created by boxes, which implies the initial containing block—being a rectangle, not a box—can’t create one.

So would it be correct to say that the initial containing block establishes a block formatting context for the root element? And that the root element also establishes a new block formatting context, as evidenced by its containment of floats?

And, assuming that the ICB does establish the first block formatting context, is it weird that the root element’s box establishes a new block formatting context even though it “doesn’t have to”?