This method adds a straight arrow that points to
        @var{TIPLOC}, which is a tuple of integers. @var{TAIL}
        specifies the starting point of the arrow. It is either None
        or a string consisting of the following letters: 'l', 'c',
        'r', 't', 'm,', and 'b'.  Letters 'l', 'c', or 'r' means to
        start the arrow from the left, center, or right of the text
        box, respectively. Letters 't', 'm', or 'b' means to start the
        arrow from the top, middle or bottom of the text box.  For
        example, when @samp{tail = 'tc'} then arrow is drawn from
        top-center point of the text box. ARROW specifies the style of
        the arrow. <<arrow>>.

def add_arrow(self, tipLoc, tail=None, arrow=arrow.default):
        """This method adds a straight arrow that points to
        @var{TIPLOC}, which is a tuple of integers. @var{TAIL}
        specifies the starting point of the arrow. It is either None
        or a string consisting of the following letters: 'l', 'c',
        'r', 't', 'm,', and 'b'.  Letters 'l', 'c', or 'r' means to
        start the arrow from the left, center, or right of the text
        box, respectively. Letters 't', 'm', or 'b' means to start the
        arrow from the top, middle or bottom of the text box.  For
        example, when @samp{tail = 'tc'} then arrow is drawn from
        top-center point of the text box. ARROW specifies the style of
        the arrow. <<arrow>>.
        """
        self._arrows.append((tipLoc, tail, arrow))