# nice PS4 with elapsed seconds (to two decimal places) and subshell indication
if zmodload zsh/system; then  # to get actual pid
	setopt PROMPT_SUBST
	if (( ${terminfo[colors]:-0} >= 8 )); then
		# first color is for main shell process, second is subshell
		PS4_PID_COLORS=(cyan magenta)
		PS4='+%B${SECONDS} %F{${PS4_PID_COLORS[1+($$ != ${sysparams[pid]})]}}%N%f:%F{yellow}%i%f>%b '
	else
		PS4='+%B${SECONDS} ${sysparams[pid]} %N:%i>%b '
	fi

	# two digits after the decimal point
	typeset -g -F 2 SECONDS
	# typeset -F 2 SECONDS  # do it twice, some bug I don't understand
fi