Initialize Tag classes in alphabetic order.

    # Loads tags from given dir.

    def load_tag_classes(dirname)

      Dir[dirname+"/**/*.rb"].sort.each {|file| require(file) }

      Dir[dirname+"/**/*.rb"].each {|file| require(file) }

    end

    # Instantiates all descendants of JsDuck::Builtins::Tag

    def instantiate_tags

      JsDuck::Builtins::Tag.descendants.each do |cls|

      tag_classes.each do |cls|

        tag = cls.new()

        Array(tag.pattern).each do |pattern|

          @patterns[pattern] = tag

      end

    end

    # Returns all available Tag classes sorted alphabetically.  This

    # ensures attributes in member signatures are always rendered in

    # the same order.

    def tag_classes

      JsDuck::Builtins::Tag.descendants.sort {|a, b| a.to_s <=> b.to_s }

    end

    # Accesses tag by @name pattern

    def get_tag(name)

      @patterns[name]