Append a new guideline to the font.

            >>> guideline = font.appendGuideline((50, 0), 90)
            >>> guideline = font.appendGuideline((0, 540), 0, name="overshoot",
            >>> color=(0, 0, 0, 0.2))

        **position** must be a :ref:`type-coordinate`
        indicating the position of the guideline.
        **angle** indicates the :ref:`type-angle` of
        the guideline. **name** indicates the name
        for the guideline. This must be a :ref:`type-string`
        or ``None``. **color** indicates the color for
        the guideline. This must be a :ref:`type-color`
        or ``None``. This will return the newly created
        :class:`BaseGuidline` object.

        ``guideline`` may be a :class:`BaseGuideline` object from which
        attribute values will be copied. If ``position``, ``angle``, ``name``
        or ``color`` are specified as arguments, those values will be used
        instead of the values in the given guideline object.

def appendGuideline(self, position=None, angle=None, name=None, color=None, guideline=None):
        """
        Append a new guideline to the font.

            >>> guideline = font.appendGuideline((50, 0), 90)
            >>> guideline = font.appendGuideline((0, 540), 0, name="overshoot",
            >>> color=(0, 0, 0, 0.2))

        **position** must be a :ref:`type-coordinate`
        indicating the position of the guideline.
        **angle** indicates the :ref:`type-angle` of
        the guideline. **name** indicates the name
        for the guideline. This must be a :ref:`type-string`
        or ``None``. **color** indicates the color for
        the guideline. This must be a :ref:`type-color`
        or ``None``. This will return the newly created
        :class:`BaseGuidline` object.

        ``guideline`` may be a :class:`BaseGuideline` object from which
        attribute values will be copied. If ``position``, ``angle``, ``name``
        or ``color`` are specified as arguments, those values will be used
        instead of the values in the given guideline object.
        """
        identifier = None
        if guideline is not None:
            guideline = normalizers.normalizeGuideline(guideline)
            if position is None:
                position = guideline.position
            if angle is None:
                angle = guideline.angle
            if name is None:
                name = guideline.name
            if color is None:
                color = guideline.color
            if guideline.identifier is not None:
                existing = set([g.identifier for g in self.guidelines if g.identifier is not None])
                if guideline.identifier not in existing:
                    identifier = guideline.identifier
        position = normalizers.normalizeCoordinateTuple(position)
        angle = normalizers.normalizeRotationAngle(angle)
        if name is not None:
            name = normalizers.normalizeGuidelineName(name)
        if color is not None:
            color = normalizers.normalizeColor(color)
        identifier = normalizers.normalizeIdentifier(identifier)
        guideline = self._appendGuideline(position, angle, name=name, color=color, identifier=identifier)
        guideline.font = self
        return guideline