A line-box is an imaginary rectangle that contains all the inline boxes that make up a line in the containing block-level element.
line - box是一个假想的矩形框，包含在此块级包含元素内连成一线的所有inline box。
This property affects the vertical positioning inside a line box of the boxes generated by an inline-level element.
该属性决定一个行内元素产生的框在一个线框内垂直方向的位置。
If the float is inside a "line box," the float's upper edge is placed level with the top of the line box.
假如该浮动是在一个“行块”中，该浮动的上边界被放置在行块顶部的水平上。
If the float is inside a "line box," the float's upper edge is placed level with the top of the line box.
假如该浮动是在一个“行块”中，该浮动的上边界被放置在行块顶部的水平上。
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