I recently had to deal with GNU Emacs lsp-mode in a context where I cared a bit about its keybindings , and in the process of that ran across mention of what one could call its leader prefix, s-l. People who use GNU Emacs a lot will know what this specific 's-' notation means, but I'm not one of them, so it took me a bit of research to work it out. This is GNU Emacs' notation for 'Super', one of the theoretical extra key modifiers that you can have on keyboards.

(I suspect that lsp-mode uses s-l as its prefix on its key bindings because everything else good is taken.)

My impression is that it's normal for Unix desktop environments to have a key mapped to 'Super', often the left 'Microsoft' key; this is the case in my unusual X desktop environment. On Windows and macOS machines, you can apparently set up mappings in GNU Emacs itself as covered by Xah Lee in "Emacs Keys: Super Hyper" ( via ). This gives me a working Super key (if I remember it, which I hopefully will now) when I'm using a GUI GNU Emacs that has direct access to relatively raw key information , either locally or on a server with X forwarding.

However, things aren't so good for me if I'm using GNU Emacs in any sort of terminal window. Unlike Alt, for which there's a standard way to handle it in terminals , there appears to be no special handling for Super in either xterm or Gnome-Terminal. Super plus a regular character gives me the regular character, both locally and over SSH connections. In this environment, the only way to access Super-based bindings is with the special and awkward GNU Emacs way to add Super (and Hyper) to key sequences . For Super, this is 'C-x @ s ...', and you can see why I'm not enthused about typing it all that often. In practice, I'm more likely to invoke obscure (to me) lsp-mode things through M-x and orderless .

Fortunately, I think lsp-mode is the only thing that has Super bindings in my usual GNU Emacs environment, which means this is something I mostly won't need to care about. Given the challenges in using Super, I'll avoid any temptation to bind my own things with it. I also suspect that there's pretty much no hope for (Unix) terminal emulators and the terminal environment to add support for it, which will probably discourage other Emacs addons from using it.

(I did a crude search of all of the .el files I use and no obvious Super bindings turned up other than lsp-mode's.)