Add support for longer, compound keyboard shortcuts (more than 2 keys, e.g. "Ctrl-Shift-K", "Ctrl-Shift+K", etc.)

[life5ign]

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I spend an inordinate amount of time trying to make my keyboard shortcuts for plugins not conflict with the built-ins and/or other plugin keyboard shortcuts that I've set. I'm wondering why there is the currently limitation to only two keys total (e.g. Ctrl-Y), and no combination of meta keys (Ctrl, Shift) allowed, e.g. Ctrl-Shift-Y?

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I'd like to be able to set keyboard Shortcuts like:

Simultaneous compound shortcuts

Ctrl-Shift-<alphanumeric>
Ctrl-Space-<alphanumeric>
<Shift-Space-<alphanumeric>
<Ctrl-Space-<alphanumeric>

The Ctrl-Shift is the most important part of those suggestions.

These would all need to be depressed at the same time.

Compound Shortcuts with sequential timeout

If possible, as a further extension to increase possibilities, a timeout system like the one that exists in vim and tmux could be used, where

Ctrl-Shift + <alphanumeric>

would be used, and executed by pressing Ctrl-Shift together, releasing, and quickly pressing <alphanumeric> within the configurable timeout, similarly to how leader in vim and prefix in tmux behave.

Describe alternatives you've considered
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I know of none.

Additional context
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[sbordeyne]

I'm in the same boat. Additionally, it's pretty limiting to only have access to alphanumeric characters. Some keyboard layouts have non-alphanumeric characters and even non-ASCII characters easily accessible. For instance, being able to press Shift-@ on a French Mac keyboard would be great, or Shift->. With a few plugins, there's no combinations remaining.