Check if selected text is r/w,
        otherwise remove read-only parts of selection

def check_selection(self):
        """
        Check if selected text is r/w,
        otherwise remove read-only parts of selection
        """
        if self.current_prompt_pos is None:
            self.set_cursor_position('eof')
        else:
            self.truncate_selection(self.current_prompt_pos)