docs: add Caps Lock mod design spec

Spec for CAPS_MOD custom keycode: tap=ESC, hold=Ctrl, Shift+tap=CapsLock, Alt+tap=CapsWord, GUI+tap=Autocorrect toggle. Includes RGB indicators and feature enablement plan.
2026-04-07 23:17:01 -04:00
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+# Caps Lock Mod — Design Spec
+
+**Date:** 2026-04-07  
+**Keyboard:** Keychron Q5 Max (ANSI Encoder)  
+**Keymap:** `keyboards/keychron/q5_max/ansi_encoder/keymaps/via/`
+
+---
+
+## Summary
+
+Replace the plain `KC_CAPS` key with a smart `CAPS_MOD` custom keycode that provides
+tap-vs-hold behavior and modifier-aware tap actions. Enable Caps Word and Autocorrect
+features with RGB indicators on the Caps Lock key (LED 55).
+
+---
+
+## Behavior
+
+| Action | Result |
+|---|---|
+| Tap | Escape |
+| Hold (past tapping term) | Left Ctrl (held until release) |
+| Shift + Tap | Toggle normal Caps Lock |
+| Alt + Tap | Toggle Caps Word |
+| GUI + Tap | Toggle Autocorrect |
+
+**Priority for modifier-aware taps:** GUI → Alt → Shift → default (ESC).  
+Modifiers are checked via `get_mods()` at key release time (they remain held by the user).
+
+---
+
+## Implementation
+
+### New custom keycode
+
+```c
+CAPS_MOD  // added to enum custom_keycodes, after existing entries
+```
+
+Replaces every `KC_CAPS` in all layers of `keymap.c`.
+
+### State variables
+
+```c
+static bool     caps_mod_held            = false;
+static bool     caps_mod_ctrl_registered = false;
+static uint16_t caps_mod_timer           = 0;
+```
+
+### `process_record_user` logic
+
+**On press:**
+```c
+caps_mod_held  = true;
+caps_mod_timer = timer_read();
+```
+
+**On release:**
+```c
+if (caps_mod_ctrl_registered) {
+    unregister_code(KC_LCTL);
+    caps_mod_ctrl_registered = false;
+} else {
+    uint8_t mods = get_mods();
+    if (mods & MOD_MASK_GUI) {
+        autocorrect_toggle();
+    } else if (mods & MOD_MASK_ALT) {
+        caps_word_toggle();
+    } else if (mods & MOD_MASK_SHIFT) {
+        tap_code(KC_CAPS);
+    } else {
+        tap_code(KC_ESC);
+    }
+}
+caps_mod_held = false;
+```
+
+### `matrix_scan_user` addition
+
+```c
+if (caps_mod_held && !caps_mod_ctrl_registered
+    && timer_elapsed(caps_mod_timer) > TAPPING_TERM) {
+    caps_mod_ctrl_registered = true;
+    register_code(KC_LCTL);
+}
+```
+
+---
+
+## RGB Indicators (LED 55 — Caps Lock physical position)
+
+Added inside `rgb_matrix_indicators_advanced_user`, checked in priority order:
+
+| State | Color |
+|---|---|
+| Caps Word on | Green `(0, 200, 0)` |
+| Autocorrect on | Purple `(150, 0, 255)` |
+| Normal Caps Lock on | White `(255, 255, 255)` |
+| All off | Dark `(0, 0, 0)` |
+
+Caps Word takes visual priority over host Caps Lock because both can technically be
+active simultaneously.
+
+---
+
+## Feature Enablement
+
+### `rules.mk` additions
+```makefile
+CAPS_WORD_ENABLE = yes
+AUTOCORRECT_ENABLE = yes
+```
+
+### `config.h` addition
+```c
+#define AUTOCORRECT_MIN_LENGTH 4
+```
+
+`autocorrect_data.h` is already present in the keymap folder. QMK picks it up
+automatically when `AUTOCORRECT_ENABLE = yes` — no manual `#include` needed.
+
+---
+
+## Files Changed
+
+| File | Change |
+|---|---|
+| `keymap.c` | Add `CAPS_MOD` to enum; add state vars; add press/release logic in `process_record_user`; add scan logic in `matrix_scan_user`; add LED 55 indicators in `rgb_matrix_indicators_advanced_user`; replace all `KC_CAPS` with `CAPS_MOD` |
+| `rules.mk` | Add `CAPS_WORD_ENABLE = yes` and `AUTOCORRECT_ENABLE = yes` |
+| `config.h` | Add `AUTOCORRECT_MIN_LENGTH 4` |