Handle a width style, which can be a fractional number
        representing a percentage of available width or positive integers
        which indicate a fixed width.

def width_normalize(self, width):
        """ Handle a width style, which can be a fractional number
        representing a percentage of available width or positive integers
        which indicate a fixed width. """
        if width is not None:
            if width > 0 and width < 1:
                return int(width * self.usable_width)
            else:
                return int(width)