XPath Extractor

    The XPath extractor is a specific extractor meant to scrape
    data from pages not containing RDF information.
    Such extractor is based on a set of configurable extraction rules
    activated by a regular expression over the page URL.
    When an extraction rule is activated all the variables it defines are
    evaluated and then a NQuads template is expanded for generating statements.
    See {{{./xref/org/deri/any23/extractor/xpath/package-summary.html}Javadoc}}.