# Adds the UTF-8 representation of `c` to `self`
	#
	#     var b = new Bytes.empty
	#     b.add_char('A')
	#     b.add_char('キ')
	#     assert b.hexdigest == "41E382AD"
	fun add_char(c: Char) do
		if persisted then regen
		var cln = c.u8char_len
		var ln = length
		enlarge(ln + cln)
		items.set_char_at(length, c)
		length += cln
	end