Form Post from Firefox

report=The validator considers attributes in the xsi namespace on the
RDF/XML document element to be properties, rather than ignoring them as
properties, as it does with attributes in the xml namespace.

By not ignoring attributes in the xsi namespace you are not able to assign
an XML schema to an RDF/XML instance document.  While assigning an XML
schema is not necessary for RDF/XML you may wish to restrict the structre
and what elements are valid when creating an instance of your metadata.

BTW, the visual graph (PNG embedded) was working, but then it abruptly
stopped working, saying empty graph file.

RDF=<?xml version="1.0">
<?xml version="1.0"?>
<rdf:RDF
  xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:dc="http://purl.org/dc/elements/1.1/"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xml:base="urn:my-base:"
  xml:lang="en"
  xsi:schemaLocation="urn:my-rdf-instance my-rdf-instance.xsd"
>
  <rdf:Description rdf:about="http://www.w3.org/">
    <dc:title>World Wide Web Consortium</dc:title> 
  </rdf:Description>
</rdf:RDF>