Platform: well, these OTOH *don't* need to be flags.

src/Magnum/Platform/EmscriptenApplication.cpp

@@ -530,7 +530,7 @@ void EmscriptenApplication::exit(int) {
 }
 
 EmscriptenApplication::MouseEvent::Button EmscriptenApplication::MouseEvent::button() const {
-    return Button(1 << _event->button);
+    return Button(_event->button);
 }
 
 Vector2i EmscriptenApplication::MouseEvent::position() const {

src/Magnum/Platform/EmscriptenApplication.h

@@ -989,14 +989,9 @@ class EmscriptenApplication::MouseEvent: public EmscriptenApplication::InputEven
          * @see @ref button()
          */
         enum class Button: std::int32_t {
-            /** Left mouse button */
+            Left,       /**< Left mouse button */
-            Left = 1 << 0,
+            Middle,     /**< Middle mouse button */
-
+            Right       /**< Right mouse button */
-            /** Middle mouse button */
-            Middle = 1 << 1,
-
-            /** Right mouse button */
-            Right = 1 << 2
         };
 
         /** @brief Button */
@@ -1028,7 +1023,7 @@ class EmscriptenApplication::MouseMoveEvent: public EmscriptenApplication::Input
          *
          * @see @ref buttons()
          */
-        enum class Button: std::int32_t {
+        enum class Button: Int {
             /** Left mouse button */
             Left = 1 << 0,