Steve Losh described the [Space Cadet Shift](https://stevelosh.com/blog/2012/10/a-modern-space-cadet/) quite well. Essentially, when you tap Left Shift on its own, you get an opening parenthesis; tap Right Shift on its own and you get the closing one. When held, the Shift keys function as normal. Yes, it's as cool as it sounds, and now even cooler supporting Control and Alt as well!
Space Cadet's functionality can conflict with the default Command functionality when both Shift keys are held at the same time. See the [Command feature](feature_command.md) for info on how to change it, or make sure that Command is disabled in your `rules.mk` with:
By default Space Cadet assumes a US ANSI layout, but if your layout uses different keys for parentheses, you can redefine them in your `config.h`. In addition, you can redefine the modifier to send on tap, or even send no modifier at all. The new configuration defines bundle all options up into a single define of 3 key codes in this order: the `Modifier` when held or when used with other keys, the `Tap Modifer` sent when tapped (no modifier if `KC_TRNS`), finally the `Keycode` sent when tapped. Now keep in mind, mods from other keys will still apply to the `Keycode` if say `KC_RSFT` is held while tapping `SC_LSPO` key with `KC_TRNS` as the `Tap Modifer`.
|`SPACE_CADET_MODIFIER_CARRYOVER` |*Not defined* |Store current modifiers before the hold mod is pressed and use them with the tap mod and keycode. Useful for when you frequently release a modifier before triggering Space Cadet. |
These defines are used in the above defines internally to support backwards compatibility, so you may continue to use them, however the above defines open up a larger range of flexibility than before. As an example, say you want to not send any modifier when you tap just `SC_LSPO`, with the old defines you had an all or nothing choice of using the `DISABLE_SPACE_CADET_MODIFIER` define. Now you can define that key as: `#define LSPO_KEYS KC_LSFT, KC_TRNS, KC_9`. This tells the system to set Left Shift if held or used with other keys, then on tap send no modifier (transparent) with the `KC_9`.
