css浮动位置未定义是啥意思？

Question

最近在看css规范，在浮动这一章节有这一段不是很理解，求大神指教
But in CSS 2.1, if, within the block formatting context, there is an in-flow negative vertical margin such that the float's position is above the position it would be at were all such negative margins set to zero, the position of the float is undefined.
链接：https://www.w3.org/TR/CSS2/vi...

Answer 1

https://juejin.cn/post/694135...
这篇博文说的很详细，推荐看一下

Answer 2

可以先不用管。CSS3 都多少年了，2.1 的规范大概知道就行，不用深究。以后也不会用到 float 做横向布局，display:flex/grid 各方面都优秀得多。