def rdfa_class klass, subject, &block
  rdfa_write_block :span, {:class => klass, :about => subject}, &block if block_given?
end

def rdfa_triple predicate, object, subject=nil, &block
  if block_given?
    rdfa_write_block :span, {:property => predicate, :content => object, :about => subject}, &block 
  else
    rdfa_write :span, object, {:property => predicate, :about => subject}
  end
end

def rdfa_write_block tag, rdfa_options = {} , &block
  content = capture(&block)
  concat(rdfa_base_final(tag, content, rdfa_options), block.binding)
end

def rdfa_write tag, body, rdfa_options = {}
  content_tag(tag, body, options = rdfa_options)
end


# rdfa header
def rdfa_html
  tag(:html, options = $rdfa_namespaces,true)
end