Begins editing for the label.

def beginEdit(self):
        """
        Begins editing for the label.
        """
        if not self._lineEdit:
            return
        
        self.aboutToEdit.emit()
        
        self._lineEdit.setText(self.editText())
        self._lineEdit.show()
        self._lineEdit.selectAll()
        self._lineEdit.setFocus()