st.advance(2)
		e := st.expression()
		pack := st.findArgumentPack(e)
		return &PackExpansion{Base: e, Pack: pack}
	} else if st.str[0] == 's' && len(st.str) > 1 && st.str[1] == 'Z' {
		st.advance(2)
		off := st.off
		e := st.expression()
		ap := st.findArgumentPack(e)
		if ap == nil {
			st.failEarlier("missing argument pack", st.off-off)
		}