docs: def iso8601timestamp(T=None, nanos=True, utc=False):
  	"""Get ISO8601-formatted timestamp string."""
  	T  = time.time() if T is None else T
  	Ti = math.floor(T)
  	Tn = round((T-Ti)*1e9)
  	if Tn >= 1e9:
  		Ti += 1
  		Tn  = 0
  	
  	s  = time.gmtime(Ti)      if utc   else time.localtime(Ti)
  	f  = time.strftime("%Y%m%dT%H%M%S", s)
  	n  = ".{:09d}".format(Tn) if nanos else ""
  	tz = "Z"                  if utc   else time.strftime("%z", s)
  	return f+n+tz