SDL: Document that you may receive mouse events with SDL_PEN_MOUSEID

SDL Commits
1 
From 716c767b7e7099fb0e2fda9db59227a7e1d1d8a4 Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Tue, 12 May 2026 20:15:42 -0700
Subject: [PATCH] Document that you may receive mouse events with
 SDL_PEN_MOUSEID

---
 include/SDL3/SDL_events.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/SDL3/SDL_events.h b/include/SDL3/SDL_events.h
index 5b60e3df9ba83..ed6950ad3b1d0 100644
--- a/include/SDL3/SDL_events.h
+++ b/include/SDL3/SDL_events.h
@@ -457,7 +457,7 @@ typedef struct SDL_MouseMotionEvent
     Uint32 reserved;
     Uint64 timestamp;   /**< In nanoseconds, populated using SDL_GetTicksNS() */
     SDL_WindowID windowID; /**< The window with mouse focus, if any */
-    SDL_MouseID which;  /**< The mouse instance id in relative mode, SDL_TOUCH_MOUSEID for touch events, or 0 */
+    SDL_MouseID which;  /**< The mouse instance id in relative mode, SDL_TOUCH_MOUSEID for touch events, SDL_PEN_MOUSEID for pen events, or 0 */
     SDL_MouseButtonFlags state;       /**< The current button state */
     float x;            /**< X coordinate, relative to window */
     float y;            /**< Y coordinate, relative to window */