示意如下:

- Max Advance
advance 是
字元串基線上最左邊的點到最右邊的點之間的距離。
string
的 advance 不一定是它所有字元的 advance 之和。這個不是字元屬性嗎?
Max Ascent
* Determines the maximum ascent of the <code>Font</code> described by
* this <code>FontMetrics</code> object. No character extends further
* above the font's baseline than this height.
Max Descent
* Determines the maximum descent of the <code>Font</code> described by
* below the font's baseline than this height.