for (var d of xdmp.collectionProperties(
                   ["http://example.com/col1/",
                    "http://example.com/col2/"])) {
  if ( d.root.xpath("/property::cpf:error",
                    {"cpf": "http://marklogic.com/cpf"}) ) {
    xdmp.nodeUri(d);
  };
};

  => A list of document URIs of documents that have a
     cpf:error property in their corresponding properties
     documents.  For example:

     http://example.com/bar.xml http://example.com/baz.xml