View source for Drag and drop topics

Topic table supports also drag and drop feature. Topics are dragged from a topic table with '''LEFT''' mouse button. Table's border is emphasized during a drag. Dragged topics can be dropped to other topic tables or even external application if the application supports drop feature. When topics are dropped into a topic table in Wandora, the behavior depends on target table type:

* If topics are dropped to the '''instance''' table, all dropped topics are made instances of the current topic. After drop the '''instance''' table should contain also dropped topics.
* If topics are dropped to the '''class''' table, all dropped topics are made classes of the current topic. After drop the '''class''' table should dropped topics also.
* If topics are dropped to the '''association''' table, new association are created with dropped topics. The cell where drop takes place has a special importance. The cell contains a player of the association and is replaced by each dropped topic in created associations.