html - 为什么float元素不会计算为div高度的一部分？BFC可以!CSS规范哪里说的？

Question

我知道 float 元素不是正常流。但是规范说非正常流不会计算为父框高度的一部分。我在 css1.0 specification 中搜索这个和 css2.0 specification

当父框成为 BFC( block 格式化上下文)时， float 元素将被计算为 BFC 的一部分。但是，我也找不到规范中所说的 float 元素将作为一部分进行计算的地方。

这个问题让我困惑了很多年，虽然我知道BFC可以解决div的高度塌陷，但是，我不知道为什么？

Answer 1

从 CSS 2.2 9.5 Floats 中的声明推断出普通包含 block 不会增加高度来包围它们的 float 的规范。它说:

Since a float is not in the flow, non-positioned block boxes created before and after the float box flow vertically as if the float did not exist.

加上 Neeraj 已经说过的话:10.6.3 Block-level non-replaced elements in normal flow when 'overflow' computes to 'visible'

Only children in the normal flow are taken into account (i.e., floating boxes and absolutely positioned boxes are ignored, and relatively positioned boxes are considered without their offset).

规范中要求 BFC 包含 float 的部分是 CSS 2.2 10.6.7 'Auto' heights for block formatting context roots它说:

In addition, if the element has any floating descendants whose bottom margin edge is below the element's bottom content edge, then the height is increased to include those edges. Only floats that participate in this block formatting context are taken into account, e.g., floats inside absolutely positioned descendants or other floats are not.