edit.addPerform( new EditSetTimelineLength( this, Session.this, selSpan.getLength() ));
edit.addPerform( TimelineVisualEdit.select( this, Session.this, selSpan.shift( -selSpan.start )));
edit.perform();
edit.end();
getUndoManager().addEdit( edit );
success = true;
}
finally {
if( !success ) edit.cancel();