From CSS 2.1,
A block container box either contains only block-level boxes or establishes an inline formatting context and thus contains only inline-level boxes.
That disappeared from CSS Display. It defines block container as
A box whose contents participate in a block formatting context.
But if the box container only contains inline-level boxes, the box container will establish an inline formatting context, and the inline-level boxes will then participate in an inline formatting context, not in a block formatting context. In fact, that's what inline-level boxes do by definition, they participate in an inline formatting context.
From CSS 2.1,
That disappeared from CSS Display. It defines block container as
But if the box container only contains inline-level boxes, the box container will establish an inline formatting context, and the inline-level boxes will then participate in an inline formatting context, not in a block formatting context. In fact, that's what inline-level boxes do by definition, they participate in an inline formatting context.