[yt-users] title of PlotCollection

Hi, I'm trying to add a title for the picture, but I can't find the right command to do so. Here is the code: pf = load(fn) halos = HaloFinder(pf) pc = PlotCollection(pf, [pos_x, pos_y, pos_z]) p = pc.add_slice("Density", 0) pc.set_width(3*rad, '1') p.modify["hop_particles"](halos, max_number=100, alpha=0.3) p.modify["title"](halos, text='z=%.2f'%z) And there is some error reported for the last line. The meaning of the error is more than one name is given to the title. Then I replace it with: p.modify["text"](halos, pos=(0.02, 0.98), text='z=%.2f'%z) But it still has error. Could someone please help me about it? Pengfei