It is a bit inconsistent that keys are described as C-x and <return> but <C-return>. It would be more logical to write C-<return>. The key parser will happily accept either, but descriptions without modifiers in <> brackets are more legible, and the result is easier to understand and explain.

Attached is a patch which adapts the code that pretty-prints keys. This is a change for human consumption only; it seems unlikely to affect compatibility. With the patch, <C-M-backspace> is now printed as C-M-<backspace>.

I'd be happy to update the manuals accordingly, and add a NEWS entry if required.