soooo just finally upgraded from an ancient version of cider and realized that I can no longer use C-c M-o to clear the buffer. Is there a replacement mapping for cider-repl-clear-buffer?

and, when/why was this changed?

I believe it's C-c C-o to clear most recent output. And with a prefix it clears everything.

@malabarba: thanks I tried this but it didn’t work for me—I think I don’t understand what “with a prefix” means, can you explain?

C-u C-c C-o

That works @malabarba, thanks—but what is “C-u”? I guess I must have missed the explanation of what prefix is somewhere along the line.

ah, found it…I’ve been ignorant of this all these years! http://stackoverflow.com/a/32683644

Indeed.

A lot of functions throughout emacs behave differently with a prefix argument

C-u is the universal prefix

There are also numerical prefixes with C-1, C-2, etc

If you google it you'll probably gfind a lot about it on the emacs manual