Semantic Data Extractor fails on non-standard attribute

I like, and use, the Semantic Data Extractor at
http://www.w3.org/2003/12/semantic-extractor.html.

Recently, I have modified my webpages in two ways. First, I have switched
to HTML 5. Second, I have added more features from the third-party service
AddThis (addthis.com). My newly modified webpages produce an exception
error in the Xerces (?) parser of the Semantic Data Extractor, and I cannot
use the tool. (Full error message is below.)

While my personal HTML and CSS is "valid" HTML 5/ CSS 3, AddThis uses a
non-standard attribute in some anchor elements, addthis:userid=[value].
With SGML-based markup, the solution is simple: load the XML schema and the
parser is happy. To the best of my knowledge, HTML 5 does not have any
mechanism for this. Therefore, the parser throws an exception.

The website says, "More Semantics ? If you have suggestion to improve this
XSLT, please send patches to public-qa-dev@w3.org." I don't know enough
about programming to offer a patch or a solution, sorry.

Hunter

Full error message when I enter the URL http://www.hunterthinks.com/my-life/
-----------------------------------------

Using org.apache.xerces.parsers.SAXParser
Exception net.sf.saxon.trans.XPathException:
org.xml.sax.SAXParseException; systemId:
http://services.w3.org/tidy/tidy?docAddr=http%3A%2F%2Fwww.hunterthinks.com%2Fmy-life%2F&passThroughXHTML=1;
lineNumber: 96; columnNumber: 144; The prefix "addthis" for attribute
"addthis:userid" associated with an element type "a" is not bound.
org.xml.sax.SAXParseException; systemId:
http://services.w3.org/tidy/tidy?docAddr=http%3A%2F%2Fwww.hunterthinks.com%2Fmy-life%2F&passThroughXHTML=1;
lineNumber: 96; columnNumber: 144; The prefix "addthis" for attribute
"addthis:userid" associated with an element type "a" is not bound.