blog post: http://autonomousmachine.com/2008/10/1/simple-rspec-markup-matcher

match_markup.rb

module Spec
  module Matchers
    module Markup
      class MatchMarkup
        def initialize(expected)
          @expected = expected
        end

        def matches?(target)
          @target = target
          standardize(@target).eql?(standardize(@expected))
        end

        def failure_message
          "expected\n#{@target}\nto match\n#{@expected}"
        end

        def negative_failure_message
          "expected\n#{@target}\nto not match\n#{@expected}" 
        end

        # alphabetize the order of attributes
        def standardize(markup)
          clean_whitespace(markup).gsub(/( [a-zA-Z_]*="[^"])+"/) do |match|
            ' ' + match.strip!.split(' ').sort.join(' ')
          end
        end

        def clean_whitespace(markup)
          markup.
          gsub(/\s+/, ' '). # cleanup whitespace
          gsub(/>\s/, '>'). # kill space after tags
          gsub(/\s</, '<'). # space before tags
          gsub(/\s\/>/, '/>'). # space inside self-closing tags
          strip
        end
      end

      def match_markup(markup)
        MatchMarkup.new(markup)
      end
    end
  end
end