docs/feature_advanced_keycodes.md


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# Advanced Keycodes

Your keymap can include keycodes that are more advanced than normal, for example keys that switch layers or send modifiers when held, but send regular keycodes when tapped. This page documents the functions that are available to you.

### Assigning Custom Names

People often define custom names using `#define`. For example:

```c
#define FN_CAPS LT(_FL, KC_CAPSLOCK)
#define ALT_TAB LALT(KC_TAB)
```

This will allow you to use `FN_CAPS` and `ALT_TAB` in your `KEYMAP()`, keeping it more readable.

### Limits of These Aliases

Currently, the keycodes able to used with these functions are limited to the [Basic Keycodes](keycodes_basic.md), meaning you can't use keycodes like `KC_TILD`, or anything greater than 0xFF. For a full list of the keycodes able to be used see [Basic Keycodes](keycodes_basic.md).

# Switching and Toggling Layers

These functions allow you to activate layers in various ways. Note that layers are not generally independent layouts -- multiple layers can be activated at once, and it's typical for layers to use `KC_TRNS` to allow keypresses to pass through to lower layers. For a detailed explanation of layers, see [Keymap Overview](keymap.md#keymap-and-layers)

* `DF(layer)` - switches the default layer. The default layer is the always-active base layer that other layers stack on top of. See below for more about the default layer. This might be used to switch from QWERTY to Dvorak layout. (Note that this is a temporary switch that only persists until the keyboard loses power. To modify the default layer in a persistent way requires deeper customization, such as calling the `set_single_persistent_default_layer` function inside of [process_record_user](custom_quantum_functions.md#programming-the-behavior-of-any-keycode).)
* `MO(layer)` - momentarily activates *layer*. As soon as you let go of the key, the layer is deactivated. 
* `LM(layer, mod)` - Momentarily activates *layer* (like `MO`), but with modifier(s) *mod* active. Only supports layers 0-15 and the left modifiers.
* `LT(layer, kc)` - momentarily activates *layer* when held, and sends *kc* when tapped.
* `TG(layer)` - toggles *layer*, activating it if it's inactive and vice versa