翻译题！
The TEXTMETRIC structure also includes a field named tmExternalLeading, which is not included in the tmHeight value. This is an amount of space that the designer of the font suggests be added between successive rows of displayed text. You can accept or reject the font designer's suggestion for including external leading when spacing lines of text. In the system fonts that I've encountered recently, tmExternalLeading has been zero, which is why I didn't include it in Figure 4-3. (Despite my vow not to tell you the dimensions of a system font, Figure 4-3 is accurate for the system font that Windows uses by default for a 640 by 480 display.)
TEXTMETRIC结构还包括一个不包含在tmHeight值中的字段tmExternalLeading。它是字体设计者建议加在横向字符之间的空间大小。在安排文字行之间的空隙时，您可以接受设计者建议的值，也可以拒绝它。在系统字体中tmExternalLeading可以为0，因此我没有在图4-3中显示它。（尽管我不想告诉你们，图4-3确实就是Windows在640×480的显示分辨率中使用的系统字体。）
中文版不靠谱啊！
[解决办法]
自己能看英文就最好
[解决办法]
字体设计者建议在文本显示的连续行之间（即上下两行之间）留有足够的空间
[解决办法]
这个值是在文本中相邻两行之间，字体设计者所建议的留有的空白空间的大小
