clipboard -- a gtk:clipboard object
selection -- a gtk:selection-data instance in which the requested data should be stored
info -- an unsigned integer with the info field corresponding to the requested target from the target entries passed to the gtk:clipboard-set-with-data function

A callback function that will be called to provide the contents of the selection. If multiple types of data were advertised, the requested type can be determined from the info parameter or by checking the target field of the selection argument. If the data could successfully be converted into then it should be stored into the selection argument by calling the gtk:selection-data-set function, or related functions such as the gtk:selection-data-set-text function. If no data is set, the requestor will be informed that the attempt to get the data failed.