code: private int pollModifierFlags() {
      return modifierFlags(
        isKeyDown(GLFW_KEY_LEFT_ALT)     || isKeyDown(GLFW_KEY_LEFT_ALT),
        isKeyDown(GLFW_KEY_LEFT_CONTROL) || isKeyDown(GLFW_KEY_RIGHT_CONTROL),
        isKeyDown(GLFW_KEY_LEFT_SUPER)   || isKeyDown(GLFW_KEY_RIGHT_SUPER),
        isKeyDown(GLFW_KEY_LEFT_SHIFT)   || isKeyDown(GLFW_KEY_RIGHT_SHIFT));
    }
docs: Returns the current state of the modifier keys. Note: the code assumes the current state of
  the modifier keys is "correct" for all events that have arrived since the last call to
  update; since that happens pretty frequently, 60fps, that's probably good enough.