doc add explanation missing from per context provate data
Signed-off-by: Andy Green <andy.green@linaro.org>
diff --git a/lib/libwebsockets.h b/lib/libwebsockets.h
index 77afd84..8b98d90 100644
--- a/lib/libwebsockets.h
+++ b/lib/libwebsockets.h
@@ -546,6 +546,9 @@
* @per_session_data_size: Libwebsockets will auto-malloc this much
* memory for the use of the extension, a pointer
* to it comes in the @user callback parameter
+ * @per_context_private_data: Optional storage for this externsion that
+ * is per-context, so it can track stuff across
+ * all sessions, etc, if it wants
*/
struct libwebsocket_extension {