一个补集合可以匹配换行符，除非换行符被指定为补集合中的一个字符。 这不同 于某些象“grep”的程序对正则表达式的处理。

contrast to the handling of regexps in programs such as `grep'.

youdao

随后使用换行符前面的最后6个字符再加上制表符来替换换行符前面的所有行内容。

We then substitute all of the line up to the newline with the last six characters before the newline plus a TAB character.

youdao

Usually with just two, maybe three characters, a character that you can't really see as well on the screen, otherwise, so a new line character.

通常需要两到三个字符，这些字符你们在屏幕上是,看不到的，这个是换行字符。

哈佛公开课 - 计算机科学课程节选