Type C-j
[bound by default to electric-newline-and-maybe-indent
], or C-q C-j
[just a plain hard return], to insert a hard return when using the multiple-cursors
library. The readme.md file contains the following excerpt:
To get out of multiple-cursors-mode, press <return> or C-g.
The latter will first disable multiple regions before disabling multiple cursors.
If you want to insert a newline in multiple-cursors-mode, use C-j.
Magnar most definitely intended that the return/enter key would exit multiple-cursors-mode
; i.e., it is bound to multiple-cursors-mode
which causes the minor-mode to turn off if it was active:
https://github.com/magnars/multiple-cursors.el/blob/master/multiple-cursors-core.el#L468
See also https://github.com/magnars/multiple-cursors.el/blob/master/multiple-cursors-core.el#L534 to examine the if/then statement.