def parse(selector_string)
            partial_match = expect_match SELECTOR, selector_string
            @type, @classes = expect_pandoc_type partial_match

            while continue_parsing? partial_match
                operator = expect partial_match, :operator
                distance = expect_integer partial_match, :distance 
                type, classes = expect_pandoc_other_type partial_match

                @relations.push Relation.new(operator, distance, type, classes)

                partial_match = rest partial_match
            end
        end
def parse(selector_string)
            partial_match = expect_match SELECTOR, selector_string
            @type, @classes = expect_pandoc_type partial_match

            while continue_parsing? partial_match
                operator = expect partial_match, :operator
                distance = expect_integer partial_match, :distance 
                type, classes = expect_pandoc_other_type partial_match

                @relations.push Relation.new(operator, distance, type, classes)

                partial_match = rest partial_match
            end
        end
Parse the selector_string to construct this Selector