See keycode table in [`doc/keycode.txt`](./keycode.txt) for description of keycodes.
In regard to implementation side most of keycodes are identical with [HID usage][HID_usage](pdf) sent to host for real and some virtual keycodes are defined to support special actions.
-[HID_usage]: http://www.usb.org/developers/devclass_docs/Hut1_11.pdf
+[HID_usage]: http://www.usb.org/developers/hidpage/Hut1_12v2.pdf
+### 3.5 Momentary switching with Modifiers
+This registers modifier key(s) simultaneously with layer switching.
+
+ ACTION_LAYER_MODS(2, MOD_LSFT | MOD_LALT)
+
+
+
## 4. Tapping
Tapping is to press and release a key quickly. Tapping speed is determined with setting of `TAPPING_TERM`, which can be defined in `config.h`, 200ms by default.