private boolean hasUnsupportedVersion(Attributes atts) {
        String version = atts.getValue("", "version");
        return "1.0".equals(version) || "1.2".equals(version);
    }
@see nu.validator.checker.Checker#startElement(java.lang.String,
     java.lang.String, java.lang.String, org.xml.sax.Attributes)
src/nu/validator/checker/UncheckedSubtreeWarner.java