元素的高度由其子元素确定（除非明确设置）。例如：

The height of an element is determined by its child elements (unless it is explicitly set). E.g.:

+------A------+
|+-----------+|
||     B     ||
|+-----------+|
|+-----------+|
||     C     ||
|+-----------+|
+-------------+

of A取决于它的孩子C的下边界的位置。

The height of A is determined by where the lower border of its child C is.

现在，浮动元素不计入父母的高度，它们被取出常规流程：

Now, floating elements do not count towards the height of their parents, they're taken out of the regular flow:

+------A------+
+--+---------++
   |    B    |
   +---------+
   +---------+
   |    C    |
   +---------+

A元素折叠为

介绍清除元素以恢复正确的高度：

Clearing elements are introduced to restore the correct height:

+------A------+
|  +---------+|
|  |    B    ||
|  +---------+|
|  +---------+|
|  |    C    ||
|  +---------+|
|+-----D-----+|
+-------------+

元素是具有 clear 属性集的零高度元素。这会导致它低于浮动元素（它清除它们）。这导致A有一个普通的子元素来计算它的高度。这是最典型的用例。

The D element is a zero-height element with the clear attribute set. That causes it to fall below the floated elements (it clears them). That causes A to have a regular child element to calculate its height by. That's the most typical use case at least.

引入额外的HTML元素的更好的解决方案是将A设置为 overflow：hidden 虽然。这具有强制高度计算的效果，其具有将高度增长到期望尺寸的相同效果。这个解决方案可能有也可能没有其他副作用。

The often better solution to introducing extra HTML elements is to set A to overflow: hidden though. That has the effect of forcing a height calculation, which has the same effect of growing the height to the desired size. This solution may or may not have other side effects though.