docs: def toStringDuration (duration):
      """Returns a description of the given duration in the most appropriate
      units (e.g. seconds, ms, us, or ns).
      """
  
      table = (
          ('%dms'      , 1e-3, 1e3),
          (u'%d\u03BCs', 1e-6, 1e6),
          ('%dns'      , 1e-9, 1e9)
      )
  
      if duration > 1:
          return '%fs' % duration
  
      for format, threshold, factor in table:
          if duration > threshold:
              return format % int(duration * factor)
  
      return '%fs' % duration