visit_String

# File ext/psych/lib/psych/visitors/yaml_tree.rb, line 285
      def visit_String o
        plain = true
        quote = true
        style = Nodes::Scalar::PLAIN
        tag   = nil

        if binary?(o)
          o     = [o].pack('m0')
          tag   = '!binary' # FIXME: change to below when syck is removed
          #tag   = 'tag:yaml.org,2002:binary'
          style = Nodes::Scalar::LITERAL
          plain = false
          quote = false
        elsif o =~ /\n(?!\Z)/  # match \n except blank line at the end of string
          style = Nodes::Scalar::LITERAL
        elsif o == '<<'
          style = Nodes::Scalar::SINGLE_QUOTED
          tag   = 'tag:yaml.org,2002:str'
          plain = false
          quote = false
        elsif @line_width && o.length > @line_width
          style = Nodes::Scalar::FOLDED
        elsif o =~ /^[^[:word:]][^"]*$/
          style = Nodes::Scalar::DOUBLE_QUOTED
        elsif not String === @ss.tokenize(o) or /\A0[0-7]*[89]/ =~ o
          style = Nodes::Scalar::SINGLE_QUOTED
        end

        is_primitive = o.class == ::String
        ivars = is_primitive ? [] : o.instance_variables

        if ivars.empty?
          unless is_primitive
            tag = "!ruby/string:#{o.class}"
            plain = false
            quote = false
          end
          @emitter.scalar o, nil, tag, plain, quote, style
        else
          maptag = '!ruby/string'.dup
          maptag << ":#{o.class}" unless o.class == ::String

          register o, @emitter.start_mapping(nil, maptag, false, Nodes::Mapping::BLOCK)
          @emitter.scalar 'str', nil, nil, true, false, Nodes::Scalar::ANY
          @emitter.scalar o, nil, tag, plain, quote, style

          dump_ivars o

          @emitter.end_mapping
        end
      end