Overloads when a mouse press occurs.  If in editable mode, and the
        click occurs on a selected index, then the editor will be created
        and no selection change will occur.

        :param      event | <QMousePressEvent>

def mousePressEvent(self, event):
        """
        Overloads when a mouse press occurs.  If in editable mode, and the
        click occurs on a selected index, then the editor will be created
        and no selection change will occur.

        :param      event | <QMousePressEvent>
        """
        item = self.itemAt(event.pos())
        column = self.columnAt(event.pos().x())

        mid_button = event.button() == QtCore.Qt.MidButton
        ctrl_click = event.button() == QtCore.Qt.LeftButton and \
                     event.modifiers() == QtCore.Qt.ControlModifier

        if item and column != -1:
            self._downItem   = weakref.ref(item)
            self._downColumn = column
            self._downState  = item.checkState(column)

        elif not item:
            self.setCurrentItem(None)
            self.clearSelection()

        if (mid_button or ctrl_click) and item and column != -1:
            self.itemMiddleClicked.emit(item, column)

        index = self.indexAt(event.pos())
        sel_model = self.selectionModel()

        if self.isEditable() and index and sel_model.isSelected(index):
            sel_model.setCurrentIndex(index, sel_model.NoUpdate)
            self.edit(index, self.SelectedClicked, event)
            event.accept()
        else:
            super(XTreeWidget, self).mousePressEvent(event)