copy-region-as-killThe copy-region-as-kill function copies a region of text from a
buffer and (via either kill-append or kill-new) saves it
in the kill-ring.
If you call copy-region-as-kill immediately after a
kill-region command, Emacs appends the newly copied text to the
previously copied text. This means that if you yank back the text, you
get it all, from both this and the previous operation. On the other
hand, if some other command precedes the copy-region-as-kill,
the function copies the text into a separate entry in the kill ring.