*
* Use the \ref gras_userdata_new macro to create a new user data (or malloc it
* and use \ref gras_userdata_set yourself), and \ref gras_userdata_get to
*
* Use the \ref gras_userdata_new macro to create a new user data (or malloc it
* and use \ref gras_userdata_set yourself), and \ref gras_userdata_get to