In addition to the primary selection, the X Window System provides a second similar facility known as the secondary selection. Nowadays, few X applications make use of the secondary selection, but you can access it using the following Emacs commands:
mouse-set-secondary). The selected text is highlighted, using the
secondary-selectionface, as you drag. The window scrolls automatically if you drag the mouse off the top or bottom of the window, just like
mouse-set-region(see Mouse Commands).
This command does not alter the kill ring.
mouse-secondary-save-then-kill). This also puts the selected text in the kill ring. A second M-mouse-3 at the same place kills the secondary selection just made.
Double or triple clicking of M-mouse-1 operates on words and lines, much like mouse-1.
mouse-yank-at-point is non-
nil, M-mouse-2 yanks
at point. Then it does not matter precisely where you click, or even
which of the frame's windows you click on. See Mouse Commands.