User:Dinoallo
From Gentoo Wiki
Tricks
Emacs
ebuild-mode
If you are using ivy instead of ido, when encountering completing-read prompt(like selecting eclasses, USE flags), ivy doesn't allow an empty selection. To indicate that you are done entering keywords, press C-M-j . Alternatively, you can make the prompt line selectable with (setq ivy-use-selectable-prompt t).