I guess the main question here is whether we should support space as seperators for boolean arguments as well. I'm not really sure if it's possible to dissambiguate e.g. % notmuch show --decrypt false friends It's not clear if false is a search term or an argument to decrypt. Personally I can live with requiring = or : for cases where a boolean option needs to be set. The other issue is completion. I guess this probably breaks bash / zsh completion (or at least using ' ' does); I have not tested.