# Attempt to parse a link reference
	#
	# Return how many characters were parsed as a reference.
	# Returns 0 if none.
	fun parse_reference(input: String): Int do
		self.input = input
		self.index = 0
		self.column = 0
		var dest
		var title
		var match_chars
		var start_index = index

		# label
		match_chars = parse_link_label
		if match_chars == 0 then return 0
		advance match_chars

		var raw_label = input.substring(0, match_chars)

		# colon
		if peek != ':' then return 0
		advance 1

		# link url
		spnl

		dest = parse_link_destination.first
		if dest == null or dest.is_empty then return 0

		var before_title = index
		var before_column = column
		spnl
		title = parse_link_title
		if title == null then
			# rewind before spaces
			index = before_title
			column = before_column
		end

		var at_line_end = true
		if index != input.length and match(re_line_end) == null then
			if title == null then
				at_line_end = false
			else
				# the potential title we found is not at the line end,
				# but it could still be a legal link reference if we discard the title
				title = null
				# rewind before spaces
				index = before_title
				column = before_column
				# and instead check if the link URL is at the line end
				at_line_end = match(re_line_end) != null
			end
		end

		if not at_line_end then return 0

		var normalized_label = raw_label.normalize_reference
		if normalized_label.is_empty then return 0

		if not reference_map.has_key(normalized_label) then
			var link = new MdLink(new MdLocation(0, 0, 0, 0), dest, title)
			reference_map[normalized_label] = link
		end

		return index - start_index
	end