A 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 @selection_data. If the data could successfully be converted into
then it should be stored into the @selection_data object by
calling gtk_selection_data_set() (or related functions such
as gtk_selection_data_set_text()). If no data is set, the requestor
will be informed that the attempt to get the data failed.
A 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 @selection_data. If the data could successfully be converted into then it should be stored into the @selection_data object by calling gtk_selection_data_set() (or related functions such as gtk_selection_data_set_text()). If no data is set, the requestor will be informed that the attempt to get the data failed.