Re: [csswg-drafts] [CSS2] Clarify margin collapsing behavior (#11306)

Ok, I think I understand where we are misaligned.

When you say:

> But the definition is more like, given an element E, we say that margins can collapse through E if the top (block-start) and bottom (block-end) margins of E are adjoining.

This statement can be interpreted in two ways:

1. Given an element E, we say that margins can collapse through E if the top margin of E is adjoining the bottom margin of E (i.e., margins within the same element).

2. Given an element E, we say that margins can collapse through E if the top margin of E adjoins some margin external to E and the bottom margin of E adjoins another margin external to E.

The conditions for 1 are stated:

>Two margins are adjoining if and only if: 
> * both belong to vertically-adjacent box edges, i.e. form one of the following pairs: 
     - top and bottom margins of a box that does not establish a new block formatting context and that has zero computed ['min-height'](https://www.w3.org/TR/CSS2/visudet.html#propdef-min-height), zero or 'auto' computed ['height'](https://www.w3.org/TR/CSS2/visudet.html#propdef-height), and no in-flow children

You say that the conditions for 2 are implied by transitivity, specifically through the statement:

>A collapsed margin is considered adjoining to another margin if any of its component margins is adjoining to that margin. 

I find this statement somewhat unclear. Should it be interpreted as:

A collapsed margin is considered adjoining to another margin M if any of the component margins of the **collapsed margin** is adjoining to M.

What exactly are the "component margins" of a collapsed margin? Does this simply refer to the individual margins that participated in the collapse?

If that’s the case, is the statement essentially saying: margin M adjoins a collapsed margin if M adjoins one of the margins that contributed to the collapse?

If so, how does this establish the condition for M "collapsing through" the collapsed margin?

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Received on Monday, 2 December 2024 20:30:42 UTC