# Write a map header for `len` key/value pairs, max of 0x0F pairs
	#
	# After writing the header, clients should write the map data, alternating
	# between keys and values.
	#
	# Require: `len <= 0x0F`
	fun write_msgpack_fixmap(len: Int)
	do
		assert len <= 0x0F
		write_byte 0b1000_0000 | len
	end