行高的基准点

[xfq]

https://w3c.github.io/clreq/#n010 :

Line height is the distance between two adjacent lines measured from their reference points. The reference point differs from implementation to implementation. However, in vertical writing mode, the horizontal center of the character frame is usually used, and with horizontal writing mode, the vertical center of the character frame is used.

行高就是彼此邻接的两行之基准点间的距离。基准点依照处理方式而会有所不同，直排时为行左右的中央线，横排时为行上下的中央线。

英文的意思是行高的基准点有多种算法，通常会选择中央线，而中文隐含着基准点只可能是中央线（没有翻译出“usually”），需要统一一下。