Users of Sublime Text might already be familiar with this concept.
Multiple cursors allow actions to be done in multiple places at once. These include insertion, deletion and replacement of characters or text.
As is well known, a cursor can be set by clicking onto the desired position in the text. Dragging the mouse while holding the mouse-button pressed results in a selection being made from the initial clicking point to the final position when the button is released. With this patch, a new cursor or selection can be added by holding CTRL while doing the operation. Same has been implemented for double-clicking(select word).
Selections and cursors can also be removed. This is done by CTRL-clicking the selection or cursor to get rid off. (Not sure how other editors like Sublime do this, but this seems good enough for an initial implementation)