Retrieving the selection is an asynchronous process. To start the
process, you call this function.
This converts the selection into the form specified by target. If
at all possible, the time field should be the time from the event
that triggered the selection. This helps make sure that events
occur in the order that the user requested them. However, if it is
not available (for instance, if the conversion was triggered by a
"clicked" signal), then you can omit it altogether. This will
cause it to be set to GDK.CurrentTime.
When the selection owner responds to the request, a
"selection_received" signal is sent to your application. The
handler for this signal receives a pointer to a GTK.SelectionData
object.
The special target TARGETS generates a list of all valid targets.
Selection defaults to PRIMARY, and target defaults to STRING.