# Write a map header for `len` key/value pairs, max of 0xFFFF_FFFF pairs
	#
	# After writing the header, clients should write the map data, alternating
	# between keys and values.
	#
	# Require: `len <= 0xFFFF_FFFF`
	fun write_msgpack_map32(len: Int)
	do
		assert len <= 0xFFFF_FFFF
		write_byte 0xDF
		write_bytes len.to_bytes(n_bytes=4)
	end