How to enter splits without mouse?

I couldn't figure out how to enter splits without having to resort to the
mouse (I'm using a Mac with the new Preview MD). The manual says that cmd-L
opens the splits window. Figured out that once the splits window was open, a
cmd-N would make another split. But: How do you put away the splits window
without having to click on the 'Done' button?

Cmd-D just deletes the current split. Enter just closes (or opens) the
current split. Couldn't find it in the manual.

Thanks for your help.
-- 
Mike Casteel
Seattle, WA