code: public void requestSystemAlertPermission() {
          if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
              try {
                  if (!isSystemAlertGranted()) {
                      Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION, Uri.parse("package:" + context.getPackageName()));
                      context.startActivityForResult(intent, OVERLAY_PERMISSION_REQ_CODE);
                  } else {
                      permissionCallback.onPermissionPreGranted(Manifest.permission.SYSTEM_ALERT_WINDOW);
                  }
              } catch (Exception ignored) {}
          } else {
              permissionCallback.onPermissionPreGranted(Manifest.permission.SYSTEM_ALERT_WINDOW);
          }
      }
docs: used only for {@link android.Manifest.permission#SYSTEM_ALERT_WINDOW}