Code use to place XMLLiteral in canonical form and preserve @Profile, @Prefix, @vocab and @lang mappings.

rdfa_xmlliteral_serialization.rb

# Add already mapped namespaces and language
@contents = contents.map do |c|
  c = Nokogiri::XML.parse(c.copy(true).to_s) if c.is_a?(LibXML::XML::Node)
  if c.is_a?(Nokogiri::XML::Element)
    c = Nokogiri::XML.parse(c.dup.to_xml(:save_with => Nokogiri::XML::Node::SaveOptions::NO_EMPTY_TAGS)).root
    # Gather namespaces from self and decendant nodes
    #
    # prefix mappings
    # Look for @xmlns and @prefix mappings. Add any other mappings from options[:prefixes]
    # that aren't already defined on this node
    defined_mappings = {}
    prefix_mappings = {}
    
    c.traverse do |n|
      ns = n.namespace
      next unless ns
      prefix = ns.prefix ? "xmlns:#{ns.prefix}" : "xmlns"
      defined_mappings[ns.prefix.to_s] = ns.href.to_s
      c[prefix] = ns.href unless c.namespaces[prefix]
    end
    
    mappings = c["prefix"].to_s.split(/\s+/)
    while mappings.length > 0 do
      prefix, uri = mappings.shift.downcase, mappings.shift
      #puts "uri_mappings prefix #{prefix} <#{uri}>"
      next unless prefix.match(/:$/)
      prefix.chop!

      # A Conforming RDFa Processor must ignore any definition of a mapping for the '_' prefix.
      next if prefix == "_"

      defined_mappings[prefix] = uri
      prefix_mappings[prefix] = uri
    end

    # Add prefixes, being careful to honor mappings defined on the element
    if options[:prefixes]
      options[:prefixes].each_pair do |p, ns|
        prefix_mappings[p] = ns.uri unless defined_mappings.has_key?(p)
      end
      if prefix_mappings.length
        c["prefix"] = prefix_mappings.keys.sort.map {|p| "#{p}: #{prefix_mappings[p]}"}.join(" ")
      end
    end
    
    # Add profiles, being careful to honor profiles defined on the element
    if options[:profiles].is_a?(Array) && options[:profiles].length > 0
      profiles = c["profile"].to_s.split(" ")
      profiles += options[:profiles]
      c["profile"] = profiles.join(" ")
    end
    
    # Add default vocabulary, being careful to honor any defined on the element
    if options[:default_vocabulary] && !c["vocab"]
      c["vocab"] = options[:default_vocabulary].to_s
    end
    
    if options[:language] && c["lang"].to_s.empty?
      c["xml:lang"] = options[:language]
    end
  end
  c.to_xml(:save_with => (Nokogiri::XML::Node::SaveOptions::NO_EMPTY_TAGS))
end.join("")