Add a little aside explaining that shifted keys with mod-tap doesn't work (#2446)

docs/feature_advanced_keycodes.md

@@ -116,7 +116,7 @@ These are the values you can use for the `mod` in `MT()` and `OSM()`:
   * 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:
 
@@ -129,6 +129,12 @@ We've added shortcuts to make common modifier/tap (mod-tap) mappings more compac
   * `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.
 
+{% hint style='info' %}
+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 modifier, any other modifiers will turn into their right equivalents, so it is not possible to "mix and match" the two.
+{% endhint %}
+
 # 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".