Add documentation for TAPPING_FORCE_HOLD (#2957) (#3320)

Also improve documentation for related settings.

docs/config_options.md

@@ -123,21 +123,23 @@ If you define these options you will enable the associated feature, which may in
 ## Behaviors That Can Be Configured
 
 * `#define TAPPING_TERM 200`
-  * how long before a tap becomes a hold
+  * how long before a tap becomes a hold, if set above 500, a key tapped during the tapping term will turn it into a hold too
 * `#define RETRO_TAPPING`
   * tap anyway, even after TAPPING_TERM, if there was no other key interruption between press and release
 * `#define TAPPING_TOGGLE 2`
   * how many taps before triggering the toggle
 * `#define PERMISSIVE_HOLD`
   * makes tap and hold keys work better for fast typers who don't want tapping term set above 500
+* `#define IGNORE_MOD_TAP_INTERRUPT`
+  * makes it possible to do rolling combos (zx) with keys that convert to other keys on hold
+* `#define TAPPING_FORCE_HOLD`
+  * makes it possible to use a dual role key as modifier shortly after having been tapped
 * `#define LEADER_TIMEOUT 300`
   * how long before the leader key times out
 * `#define ONESHOT_TIMEOUT 300`
   * how long before oneshot times out
 * `#define ONESHOT_TAP_TOGGLE 2`
   * how many taps before oneshot toggle is triggered
-* `#define IGNORE_MOD_TAP_INTERRUPT`
-  * makes it possible to do rolling combos (zx) with keys that convert to other keys on hold
 * `#define QMK_KEYS_PER_SCAN 4`
   * Allows sending more than one key per scan. By default, only one key event gets
     sent via `process_record()` per scan. This has little impact on most typing, but

docs/feature_advanced_keycodes.md

@@ -175,3 +175,31 @@ Example: (Tapping Term = 200ms)
 - 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).