Closed is a basic approximation of Emacs's ido-mode for opening files and directories. It'll pop open a panel similar to the command palette and will give you possible completions as you type paths. It'll also expand ~ for you.
alt-ctrl-pon Linux): Open a file.
While In Closed
tab): If the current selection is a file then open it otherwise complete the current path.
ctrl-enteron Linux): Open current path. If it's an existing directory, open in a new atom window, otherwise create a file.
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