# Switching and Toggling Layers
-These functions allow you to activate layers in various ways.
+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)
-* `MO(layer)` - momentary switch to *layer*. As soon as you let go of the key, the layer is deactivated and you pop back out to the previous layer.
-* `LT(layer, kc)` - momentary switch to *layer* when held, and *kc* when tapped.
-* `TG(layer)` - toggles a layer on or off.
-* `TO(layer)` - Goes to a layer. This code is special, because it lets you go either up or down the stack -- just goes directly to the layer you want. So while other codes only let you go _up_ the stack (from layer 0 to layer 3, for example), `TO(2)` is going to get you to layer 2, no matter where you activate it from -- even if you're currently on layer 5. This gets activated on keydown (as soon as the key is pressed).
-* `TT(layer)` - Layer Tap-Toggle. If you hold the key down, the layer becomes active, and then deactivates when you let go. And if you tap it, the layer simply becomes active (toggles on). It needs 5 taps by default, but you can set it by defining `TAPPING_TOGGLE`, for example, `#define TAPPING_TOGGLE 2` for just two taps.
+* `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
+* `TO(layer)` - activates *layer* and de-activates all other layers (except your default layer). This function is special, because instead of just adding/removing one layer to your active layer stack, it will completely replace your current active layers, uniquely allowing you to replace higher layers with a lower one. This is activated on keydown (as soon as the key is pressed).
+* `TT(layer)` - Layer Tap-Toggle. If you hold the key down, *layer* is activated, and then is de-activated when you let go (like `MO`). If you repeatedly tap it, the layer will be toggled on or off (like `TG`). It needs 5 taps by default, but you can change this by defining `TAPPING_TOGGLE` -- for example, `#define TAPPING_TOGGLE 2` to toggle on just two taps.
# Working with Layers
If you are just getting started with QMK you will want to keep everything simple. Follow these guidelines when setting up your layers:
-* Setup layer 0 as your "base" layer. This is your normal typing layer, and could be whatever layout you want (qwerty, dvorak, colemak, etc.)
+* Setup layer 0 as your default, "base" layer. This is your normal typing layer, and could be whatever layout you want (qwerty, dvorak, colemak, etc.). It's important to set this as the lowest layer since it will typically have most or all of the keyboard's keys defined, so would block other layers from having any effect if it were above them (i.e., had a higher layer number).
* Arrange your layers in a "tree" layout, with layer 0 as the root. Do not try to enter the same layer from more than one other layer.
-* Never try to stack a higher numbered layer on top of a lower numbered layer. Doing so is tricky and error prone.
+* In a layer's keymap, only reference higher-numbered layers. Because layers are processed from the highest-numbered (topmost) active layer down, modifying the state of lower layers can be tricky and error-prone.
### Intermediate Users
Layers stack on top of each other in numerical order. When determining what a keypress does, QMK scans the layers from the top down, stopping when it reaches the first active layer that is not set to `KC_TRNS`. As a result if you activate a layer that is numerically lower than your current layer, and your current layer (or another layer that is active and higher than your target layer) has something other than `KC_TRNS`, that is the key that will be sent, not the key on the layer you just activated. This is the cause of most people's "why doesn't my layer get switched" problem.
-Sometimes, you might want to switch between layers in a macro or as part of a tap dance routine. `layer_on` activates a layer, and `layer_off` deactivates it. More layer-related functions can be found in [action_layer.h](../tmk_core/common/action_layer.h).
+Sometimes, you might want to switch between layers in a macro or as part of a tap dance routine. `layer_on` activates a layer, and `layer_off` deactivates it. More layer-related functions can be found in [action_layer.h](https://github.com/qmk/qmk_firmware/blob/master/tmk_core/common/action_layer.h).
# Modifier Keys
* MOD_HYPR
* MOD_MEH
-These can also be combined like `MOD_LCTL | MOD_LSFT` e.g. `MT(MOD_LCTL | MOD_LSFT, KC_ESC)` which would activate Control and Shift when held, and send Escape when tapped. Note however, that you cannot mix right and left side modifiers.
+These can also be combined like `MOD_LCTL | MOD_LSFT` e.g. `MT(MOD_LCTL | MOD_LSFT, KC_ESC)` which would activate Control and Shift when held, and send Escape when tapped.
We've added shortcuts to make common modifier/tap (mod-tap) mappings more compact:
* `LCAG_T(kc)` - is CtrlAltGui when held and *kc* when tapped
* `MEH_T(kc)` - is like Hyper, but not as cool -- does not include the Cmd/Win key, so just sends Alt+Ctrl+Shift.
+?> Due to the way that keycodes are structured, any modifiers specified as part of `kc`, such as `LCTL()` or `KC_LPRN`, will only activate when held instead of tapped.
+
+?> Additionally, if there is at least one right-handed modifier, any other modifiers in a chain of functions will turn into their right-handed equivalents, so it is not possible to "mix and match" the two.
+
# One Shot Keys
One shot keys are keys that remain active until the next key is pressed, and then are released. This allows you to type keyboard combinations without pressing more than one key at a time. These keys are usually called "Sticky keys" or "Dead keys".
* `OSM(mod)` - Momentarily hold down *mod*. You must use the `MOD_*` keycodes as shown in [Mod Tap](#mod-tap), not the `KC_*` codes.
* `OSL(layer)` - momentary switch to *layer*.
-Sometimes, you want to activate a one-shot layer as part of a macro or tap dance routine. To do this, you need to call `set_oneshot_layer(LAYER, ONESHOT_START)` on key down, and `set_oneshot_layer(ONESHOT_PRESSED)` on key up. If you want to cancel the oneshot, call `reset_oneshot_layer()`. For more complicated actions, take a look at the oneshot implementation in [`process_record`](../tmk_core/common/action.c#L429).
+Sometimes, you want to activate a one-shot layer as part of a macro or tap dance routine. To do this, you need to call `set_oneshot_layer(LAYER, ONESHOT_START)` on key down, and `set_oneshot_layer(ONESHOT_PRESSED)` on key up. If you want to cancel the oneshot, call `reset_oneshot_layer()`. For more complicated actions, take a look at the oneshot implementation in [`process_record`](https://github.com/qmk/qmk_firmware/blob/master/tmk_core/common/action.c#L429).
+
+If you're having issues with OSM translating over Remote Desktop Connection, this can be fixed by opening the settings, going to the "Local Resources" tap, and in the keyboard section, change the drop down to "On this Computer". This will fix the issue and allow OSM to function properly over Remote Desktop.
-## Permissive Hold
+# Permissive Hold
As of [PR#1359](https://github.com/qmk/qmk_firmware/pull/1359/), there is a new `config.h` option:
- SHFT_T(KC_A) Up
With defaults, if above is typed within tapping term, this will emit `ax`. With permissive hold, if above is typed within tapping term, this will emit `X` (so, Shift+X).
+
+# Mod tap interrupt
+
+When a dual role key used for a modifier is quickly followed by another keys, it is interpreted as held even before the tapping term elapsed. This is a problem if a key is used for example inside a rolling combo because the second key will be pressed before the first key is released.
+
+For example, when trying to type the rolling combo "zx" and z being configured to send Ctrl when hold, z rapidly followed by x actually sends Ctrl-x. That's bad.
+
+You can disable this behavior by defining `IGNORE_MOD_TAP_INTERRUPT` in `config.h`.
+
+Note that this only concerns modifiers and not layer switching keys.
+
+# Hold after tap
+
+When the user holds a key after tap, this repeats the tapped key rather to hold a modifier key. This allows to use auto repeat for the tapped key. If you prefer to hold a modifier instead, define `TAPPING_FORCE_HOLD` in `config.h`.
+
+Example:
+
+- SHFT_T(KC_A) Down
+- SHFT_T(KC_A) Up
+- SHFT_T(KC_A) Down
+- wait more than tapping term...
+- SHFT_T(KC_A) Up
+
+With default settings, `a` will be sent on the first release, then `a` will be sent on the second press allowing the computer to trigger its auto repeat function.
+
+With `TAPPING_FORCE_HOLD`, the second press will be interpreted as a Shift, allowing to use it as a modifier shortly after having used it as a tap.
+
+!> `TAPPING_FORCE_HOLD` will break anything that uses tapping toggles (Such as the `TT` layer keycode, and the One Shot Tapping Toggle).
+
+# Retro Tapping
+
+When you hold a dual function key, and haven't pressed anything when you release the key, normally nothing happens. However, if you enable this, if you release the key without pressing another key, it will send the original key, even if it is outside of the tapping term.
+
+For instance, if you're using `LT(2, KC_SPACE)`, if you hold the key, don't hit anything else and then release it, normally, nothing happens. But with `RETRO_TAPPING` defined in your `config.h`, it will send `KC_SPACE`.
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