Re: [csswg-drafts] [css2.2] Section 9.4.1's definition of a BFC is an oversimplification (#12524)

Thank you for your perspective. I understand the argument that, from a strict specification architecture standpoint, a BFC's direct responsibility is the vertical stacking of block-level boxes.

However, I maintain that this narrow definition does not accurately describe the practical reality and full role of a Block Formatting Context. This makes the current wording a misleading oversimplification for developers who rely on the specification for a complete mental model.

Here are the key points supporting this view:

1. **Direct Containment of Line Boxes:** A BFC does not only contain block-level boxes. When it encounters inline content, it contains line boxes, which are fundamentally different from block-level boxes. While the mechanism might involve "anonymous block boxes," the practical reality is that the BFC is directly responsible for stacking these line boxes, which are themselves horizontal containers for inline content. A definition that ignores this is incomplete.
2. **Responsibility for Floats:** One of the most critical and practical uses of a new BFC is to contain floats. The BFC must know about the floats inside it to correctly determine its own height and to correctly position the in-flow block boxes around those floats. A definition that makes no mention of this primary function fails to describe what a BFC actually does.
3. **The Developer's Perspective:** A developer debugging a layout issue must consider all interacting elements within a BFC's boundary—block, inline, and floated. The final rendered layout is a result of all these systems working together. A useful definition should describe this holistic reality, not just one isolated aspect of the abstract model.

For these reasons, I believe a more precise definition is needed to provide developers with a truly accurate understanding of this foundational layout concept.

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Received on Saturday, 26 July 2025 04:33:43 UTC