比括号更自由宽松。

例子：

破折号用作中断：

His first thought on getting out of bed---if he had any thought at all---was to get back in again.

破折号用作分隔长的同位语：

The rear axle began to make a noise---a grinding, chattering, teeth-gritting rasp.

破折号用作分隔长的概述：

The increasing reluctance of the sun rise, the extra nip in the breeze, the patter of shed leaves dropping---all the evidences of fall drifting into winter were clearer each day.

但是将存折号仅用作普通的中断时，似乎并不合适。