# Check if line is a block link definition.
	# Return `true` if line contains a valid link ref and save it into `link_refs`.
	private fun check_link_ref(line: MDLine): Bool do
		var md = line.value
		var is_link_ref = false
		var id = new FlatBuffer
		var link = new FlatBuffer
		var comment = new FlatBuffer
		var pos = -1
		if not line.is_empty and line.leading < 4 and line.value[line.leading] == '[' then
			pos = line.leading + 1
			pos = md.read_until(id, pos, ']')
			if not id.is_empty and pos >= 0 and pos + 2 < line.value.length then
				if line.value[pos + 1] == ':' then
					pos += 2
					pos = md.skip_spaces(pos)
					if pos >= 0 and line.value[pos] == '<' then
						pos += 1
						pos = md.read_until(link, pos, '>')
						pos += 1
					else if pos >= 0 then
						pos = md.read_until(link, pos, ' ', '\n')
					end
					if not link.is_empty then
						pos = md.skip_spaces(pos)
						if pos > 0 and pos < line.value.length then
							var c = line.value[pos]
							if c == '\"' or c == '\'' or c == '(' then
								pos += 1
								if c == '(' then
									pos = md.read_until(comment, pos, ')')
								else
									pos = md.read_until(comment, pos, c)
								end
								if pos > 0 then is_link_ref = true
							end
						else
							is_link_ref = true
						end
					end
				end
			end
		end
		if is_link_ref and not id.is_empty and not link.is_empty then
			var lr = new LinkRef.with_title(link.write_to_string, comment.write_to_string)
			add_link_ref(id.write_to_string, lr)
			if comment.is_empty then last_link_ref = lr
			return true
		else
			comment = new FlatBuffer
			if not line.is_empty and last_link_ref != null then
				pos = line.leading
				var c = line.value[pos]
				if c == '\"' or c == '\'' or c ==  '(' then
					pos += 1
					if c == '(' then
						pos = md.read_until(comment, pos, ')')
					else
						pos = md.read_until(comment, pos, c)
					end
				end
				var last_link_ref = self.last_link_ref
				if not comment.is_empty and last_link_ref != null then
					last_link_ref.title = comment.write_to_string
				end
			end
			if comment.is_empty then return false
			return true
		end
	end