'e.g., ``bbox.splitx(f1, f2, ...)``
Returns a list of new :class:`Bbox` objects formed by
splitting the original one with vertical lines at fractional
positions *f1*, *f2*, ...'

def splitx(self, *args):

    xf = (([0] + list(args)) + [1])
    (x0, y0, x1, y1) = self.extents
    w = (x1 - x0)
    return [Bbox([[(x0 + (xf0 * w)), y0], [(x0 + (xf1 * w)), y1]]) for (xf0, xf1) in zip(xf[:(-1)], xf[1:])]
