#data
<x-y xmlns="http://www.w3.org/1999/xhtml" class="foo-bar">abc</x-y>
#errors

#data
<x-y xmlns="http://www.w3.org/1999/xhtml" title="foo-bar">abc</x-y>
#errors

#data
<x-y xmlns="http://www.w3.org/1999/xhtml" id="">abc</x-y>
#errors
/x-y/@id;empty attribute value;m

#data
<x-y xmlns="http://www.w3.org/1999/xhtml" is="foo-bar">abc</x-y>
#errors
/x-y/@is;attribute not allowed;m

#data
<x-y xmlns="http://www.w3.org/1999/xhtml" data-id="">abc</x-y>
#errors

#data
<x-y xmlns="http://www.w3.org/1999/xhtml" hoge="">abc</x-y>
#errors

#data
<x-y xmlns="http://www.w3.org/1999/xhtml" Abc="">abc</x-y>
#errors
/x-y/@Abc;attribute not defined;m