diff --git a/feature_advanced_keycodes.md b/feature_advanced_keycodes.md
index 745308b29ef..75b7fef89b5 100644
--- a/feature_advanced_keycodes.md
+++ b/feature_advanced_keycodes.md
@@ -23,6 +23,141 @@ These allow you to combine a modifier with a keycode. When pressed, the keydown
You can also chain them, for example `LCTL(LALT(KC_DEL))` or `C(A(KC_DEL))` makes a key that sends Control+Alt+Delete with a single keypress.
+# Checking Modifier State :id=checking-modifier-state
+
+The current modifier state can mainly be accessed with two functions: `get_mods()` for normal modifiers and modtaps and `get_oneshot_mods()` for one-shot modifiers (unless they're held, in which case they act like normal modifier keys).
+
+The presence of one or more specific modifiers in the current modifier state can be detected by ANDing the modifier state with a mod mask corresponding to the set of modifiers you want to match for. The reason why bitwise operators are used is that the modifier state is stored as a single byte in the format (GASC)R(GASC)L.
+
+Thus, to give an example, `01000010` would be the internal representation of LShift+RAlt.
+For more information on bitwise operators in C, click [here](https://en.wikipedia.org/wiki/Bitwise_operations_in_C) to open the Wikipedia page on the topic.
+
+In practice, this means that you can check whether a given modifier is active with `get_mods() & MOD_BIT(KC_)` (see the [list of modifier keycodes](keycodes_basic.md#modifiers)) or with `get_mods() & MOD_MASK_` if the difference between left and right hand modifiers is not important and you want to match both. Same thing can be done for one-shot modifiers if you replace `get_mods()` with `get_oneshot_mods()`.
+
+To check that *only* a specific set of mods is active at a time, AND the modifier state and your desired mod mask as explained above and compare the result to the mod mask itself: `get_mods() & == `.
+
+For example, let's say you want to trigger a piece of custom code if one-shot left control and one-shot left shift are on but every other one-shot mods are off. To do so, you can compose the desired mod mask by combining the mod bits for left control and shift with `(MOD_BIT(KC_LCTL) | MOD_BIT(KC_LSFT))` and then plug it in: `get_oneshot_mods & (MOD_BIT(KC_LCTL) | MOD_BIT(KC_LSFT)) == (MOD_BIT(KC_LCTL) | MOD_BIT(KC_LSFT))`. Using `MOD_MASK_CS` instead for the mod bitmask would have forced you to press four modifier keys (both versions of control and shift) to fulfill the condition.
+
+The full list of mod masks is as follows:
+
+| Mod Mask Name | Matching Modifiers |
+|--------------------|------------------------------------------------|
+| `MOD_MASK_CTRL` | LCTRL , RCTRL |
+| `MOD_MASK_SHIFT` | LSHIFT , RSHIFT |
+| `MOD_MASK_ALT` | LALT , RALT |
+| `MOD_MASK_GUI` | LGUI , RGUI |
+| `MOD_MASK_CS` | CTRL , SHIFT |
+| `MOD_MASK_CA` | (L/R)CTRL , (L/R)ALT |
+| `MOD_MASK_CG` | (L/R)CTRL , (L/R)GUI |
+| `MOD_MASK_SA` | (L/R)SHIFT , (L/R)ALT |
+| `MOD_MASK_SG` | (L/R)SHIFT , (L/R)GUI |
+| `MOD_MASK_AG` | (L/R)ALT , (L/R)GUI |
+| `MOD_MASK_CSA` | (L/R)CTRL , (L/R)SHIFT , (L/R)ALT |
+| `MOD_MASK_CSG` | (L/R)CTRL , (L/R)SHIFT , (L/R)GUI |
+| `MOD_MASK_CAG` | (L/R)CTRL , (L/R)ALT , (L/R)GUI |
+| `MOD_MASK_SAG` | (L/R)SHIFT , (L/R)ALT , (L/R)GUI |
+| `MOD_MASK_CSAG` | (L/R)CTRL , (L/R)SHIFT , (L/R)ALT , (L/R)GUI |
+
+Aside from accessing the currently active modifiers using `get_mods()`, there exists some other functions you can use to modify the modifier state, where the `mods` argument refers to the modifiers bitmask.
+
+* `add_mods(mods)`: Enable `mods` without affecting any other modifiers
+* `register_mods(mods)`: Like `add_mods` but send a keyboard report immediately.
+* `del_mods(mods)`: Disable `mods` without affecting any other modifiers
+* `unregister_mods(mods)`: Like `del_mods` but send a keyboard report immediately.
+* `set_mods(mods)`: Overwrite current modifier state with `mods`
+* `clear_mods()`: Reset the modifier state by disabling all modifiers
+
+Similarly, in addition to `get_oneshot_mods()`, there also exists these functions for one-shot mods:
+
+* `add_oneshot_mods(mods)`: Enable `mods` without affecting any other one-shot modifiers
+* `del_oneshot_mods(mods)`: Disable `mods` without affecting any other one-shot modifiers
+* `set_oneshot_mods(mods)`: Overwrite current one-shot modifier state with `mods`
+* `clear_oneshot_mods()`: Reset the one-shot modifier state by disabling all one-shot modifiers
+
+## Examples :id=examples
+
+The following examples use [advanced macro functions](feature_macros.md#advanced-macro-functions) which you can read more about in the [documentation page on macros](feature_macros.md).
+
+### Alt + Escape for Alt + Tab :id=alt-escape-for-alt-tab
+
+Simple example where chording Left Alt with `KC_ESC` makes it behave like `KC_TAB` for alt-tabbing between applications. This example strictly checks if only Left Alt is active, meaning you can't do Alt+Shift+Esc to switch between applications in reverse order. Also keep in mind that this removes the ability to trigger the actual Alt+Escape keyboard shortcut, though it keeps the ability to do AltGr+Escape.
+
+```c
+bool process_record_user(uint16_t keycode, keyrecord_t *record) {
+ switch (keycode) {
+
+ case KC_ESC:
+ // Detect the activation of only Left Alt
+ if ((get_mods() & MOD_BIT(KC_LALT)) == MOD_BIT(KC_LALT)) {
+ if (record->event.pressed) {
+ // No need to register KC_LALT because it's already active.
+ // The Alt modifier will apply on this KC_TAB.
+ register_code(KC_TAB);
+ } else {
+ unregister_code(KC_TAB);
+ }
+ // Do not let QMK process the keycode further
+ return false;
+ }
+ // Else, let QMK process the KC_ESC keycode as usual
+ return true;
+
+ }
+ return true;
+};
+```
+
+### Shift + Backspace for Delete :id=shift-backspace-for-delete
+
+Advanced example where the original behaviour of shift is cancelled when chorded with `KC_BSPC` and is instead fully replaced by `KC_DEL`. Two main variables are created to make this work well: `mod_state` and `delkey_registered`. The first one stores the modifier state and is used to restore it after registering `KC_DEL`. The second variable is a boolean variable (true or false) which keeps track of the status of `KC_DEL` to manage the release of the whole Backspace/Delete key correctly.
+
+As opposed to the previous example, this doesn't use strict modifier checking. Pressing `KC_BSPC` while one or two shifts are active is enough to trigger this custom code, regardless of the state of other modifiers. That approach offers some perks: Ctrl+Shift+Backspace lets us delete the next word (Ctrl+Delete) and Ctrl+Alt+Shift+Backspace lets us execute the Ctrl+Alt+Del keyboard shortcut.
+
+```c
+// Initialize variable holding the binary
+// representation of active modifiers.
+uint8_t mod_state;
+bool process_record_user(uint16_t keycode, keyrecord_t *record) {
+ // Store the current modifier state in the variable for later reference
+ mod_state = get_mods();
+ switch (keycode) {
+
+ case KC_BSPC:
+ {
+ // Initialize a boolean variable that keeps track
+ // of the delete key status: registered or not?
+ static bool delkey_registered;
+ if (record->event.pressed) {
+ // Detect the activation of either shift keys
+ if (mod_state & MOD_MASK_SHIFT) {
+ // First temporarily canceling both shifts so that
+ // shift isn't applied to the KC_DEL keycode
+ del_mods(MOD_MASK_SHIFT);
+ register_code(KC_DEL);
+ // Update the boolean variable to reflect the status of KC_DEL
+ delkey_registered = true;
+ // Reapplying modifier state so that the held shift key(s)
+ // still work even after having tapped the Backspace/Delete key.
+ set_mods(mod_state);
+ return false;
+ }
+ } else { // on release of KC_BSPC
+ // In case KC_DEL is still being sent even after the release of KC_BSPC
+ if (delkey_registered) {
+ unregister_code(KC_DEL);
+ delkey_registered = false;
+ return false;
+ }
+ }
+ // Let QMK process the KC_BSPC keycode as usual outside of shift
+ return true;
+ }
+
+ }
+ return true;
+};
+```
+
# Legacy Content :id=legacy-content
This page used to encompass a large set of features. We have moved many sections that used to be part of this page to their own pages. Everything below this point is simply a redirect so that people following old links on the web find what they're looking for.
diff --git a/feature_macros.md b/feature_macros.md
index 6e69ad642cf..3660f377559 100644
--- a/feature_macros.md
+++ b/feature_macros.md
@@ -209,7 +209,7 @@ SEND_STRING(".."SS_TAP(X_END));
There are some functions you may find useful in macro-writing. Keep in mind that while you can write some fairly advanced code within a macro, if your functionality gets too complex you may want to define a custom keycode instead. Macros are meant to be simple.
-?> You can also use the functions described in [Useful functions](ref_functions.md) for additional functionality. For example `reset_keyboard()` allows you to reset the keyboard as part of a macro.
+?> You can also use the functions described in [Useful function](ref_functions.md) and [Checking modifier state](feature_advanced_keycodes#checking-modifier-state) for additional functionality. For example, `reset_keyboard()` allows you to reset the keyboard as part of a macro and `get_mods() & MOD_MASK_SHIFT` lets you check for the existence of active shift modifiers.
### `record->event.pressed`