@classmethod
def from_text(cls, data):
    """Construct an instance from text format.

        Parameters
        ----------
            data : str
                text such as ``'Head:Na:中文字'``.

        .. note::

            - ``'Head:Na:中文字'`` -> **role** = ``'Head'``, **pos** = ``'Na'``, **word** = ``'中文字'``
            - ``'Head:Na'``       -> **role** = ``'Head'``, **pos** = ``'Na'``, **word** = ``None``
            - ``'Na'``            -> **role** = ``None``,   **pos** = ``'Na'``, **word** = ``None``
        """
    if ':' in data:
        fields = data.split(':')
        return cls(*fields)
    return cls(pos=data)
