Supporting-and-Using-Extra-Input-Messages.md

@@ -257,14 +257,18 @@ you should:
 
 1. Fill the fields of `extra` structure, e.g.:
 
+```
     extra->event = IAL_EVENT_AXIS;
     extra->wparam = MAKELONG(AXIS_SCROLL_VERTICAL, AXIS_SOURCE_WHEEL);
     extra->wparam = MAKELONG(AXIS_SCROLL_HORIZONTAL, AXIS_SOURCE_WHEEL);
     extra->lparam = MAKELONG(mouse_event->sv, mouse_event->dsv);
+```
 
 1. Make sure the return value of this operator have the bit of `IAL_EVENT_EXTRA` set:
 
+```
     retval |= IAL_EVENT_EXTRA;
+```
 
 For more information, please refer to the `libinput` and/or `random` IAL engines: