code: def cmd_z(self, lvl=None, ch=None):
          
          viewer = self.get_viewer(ch)
          if viewer is None:
              self.log("No current viewer/channel.")
              return
  
          cur_lvl = viewer.get_zoom()
  
          if lvl is None:
              self.log("zoom=%f" % (cur_lvl))
  
          else:
              viewer.zoom_to(lvl)
docs: z lvl=level ch=chname
  
          Zoom the image for the given viewer/channel to the given zoom
          level.  Levels can be positive or negative numbers and are
          relative to a scale of 1:1 at zoom level 0.