Keymap

Power key doesn't work

Use KC_PWR instead of KC_POWER or vice versa.

KC_PWR works with Windows and Linux, not with OSX.
KC_POWER works with OSX and Linux, not with Windows.

http://geekhack.org/index.php?topic=14290.msg1327264#msg1327264

Oneshot modifier

Solves my personal 'the' problem. I often got 'the' or 'THe' wrongly instead of 'The'. Oneshot Shift mitgates this for me. https://github.com/tmk/tmk_keyboard/issues/67

Modifier/Layer stuck

Modifier keys or layers can be stuck unless layer switching is configured properly. For Modifier keys and layer actions you have to place KC_TRANS on same position of destination layer to unregister the modifier key or return to previous layer on release event.

https://github.com/tmk/tmk_keyboard/blob/master/doc/keymap.md#31-momentary-switching http://geekhack.org/index.php?topic=57008.msg1492604#msg1492604

Mechanical Lock Switch Support

https://github.com/tmk/tmk_keyboard#mechanical-locking-support

This feature is for mechanical lock switch like this Alps one. http://deskthority.net/wiki/Alps_SKCL_Lock

Using enabling this feature and using keycodes LCAP, LNUM or LSCR in keymap you can use physical locking CapsLock, NumLock or ScrollLock keys as you expected.

Old vintage mechanical keyboards occasionally have lock switches but modern ones don't have. You don't need this feature in most case and just use keycodes CAPS, NLCK and SLCK.