### 3. Layer
Layer is key-action map to assign action to every physical key. You can define multiple layers in keymap and make layers active out of keymap during operation at will.
- First layer is indexed by `0` which usually become **`default layer`** and active in initial state.
+ First layer is indexed by `0` which usually become `default layer` and active in initial state.
You can define **16 layers** at most in each keymaps[] and overlays[].