static VALUE
new (VALUE klass, VALUE nodeobj)
{
  xmlNodePtr node;
  xmlXPathContextPtr ctx;
  VALUE self;

  Data_Get_Struct(nodeobj, xmlNode, node);

  xmlXPathInit();

  ctx = xmlXPathNewContext(node->doc);
  ctx->node = node;

  xmlXPathRegisterNs(ctx, NOKOGIRI_BUILTIN_PREFIX, NOKOGIRI_BUILTIN_URI);
  xmlXPathRegisterFuncNS(ctx, (const xmlChar *)"css-class", NOKOGIRI_BUILTIN_URI,
                         xpath_builtin_css_class);
  xmlXPathRegisterFuncNS(ctx, (const xmlChar *)"local-name-is", NOKOGIRI_BUILTIN_URI,
                         xpath_builtin_local_name_is);

  self = Data_Wrap_Struct(klass, 0, deallocate, ctx);
  return self;
}

static VALUE
evaluate(int argc, VALUE *argv, VALUE self)
{
  VALUE search_path, xpath_handler;
  VALUE retval = Qnil;
  xmlXPathContextPtr ctx;
  xmlXPathObjectPtr xpath;
  xmlChar *query;

  Data_Get_Struct(self, xmlXPathContext, ctx);

  if (rb_scan_args(argc, argv, "11", &search_path, &xpath_handler) == 1) {
    xpath_handler = Qnil;
  }

  query = (xmlChar *)StringValueCStr(search_path);

  if (Qnil != xpath_handler) {
    /* FIXME: not sure if this is the correct place to shove private data. */
    ctx->userData = (void *)xpath_handler;
    xmlXPathRegisterFuncLookup(ctx, lookup, (void *)xpath_handler);
  }

  xmlResetLastError();
  xmlSetStructuredErrorFunc(NULL, Nokogiri_error_raise);

  /* For some reason, xmlXPathEvalExpression will blow up with a generic error */
  /* when there is a non existent function. */
  xmlSetGenericErrorFunc(NULL, xpath_generic_exception_handler);

  xpath = xmlXPathEvalExpression(query, ctx);
  xmlSetStructuredErrorFunc(NULL, NULL);
  xmlSetGenericErrorFunc(NULL, NULL);

  if (xpath == NULL) {
    xmlErrorPtr error = xmlGetLastError();
    rb_exc_raise(Nokogiri_wrap_xml_syntax_error(error));
  }

  retval = xpath2ruby(xpath, ctx);
  if (retval == Qundef) {
    retval = noko_xml_node_set_wrap(NULL, DOC_RUBY_OBJECT(ctx->doc));
  }

  xmlXPathFreeNodeSetList(xpath);

  return retval;
}

# File lib/nokogiri/xml/xpath_context.rb, line 8
def register_namespaces(namespaces)
  namespaces.each do |k, v|
    k = k.to_s.gsub(/.*:/, "") # strip off 'xmlns:' or 'xml:'
    register_ns(k, v)
  end
end

static VALUE
register_ns(VALUE self, VALUE prefix, VALUE uri)
{
  xmlXPathContextPtr ctx;
  Data_Get_Struct(self, xmlXPathContext, ctx);

  xmlXPathRegisterNs(ctx,
                     (const xmlChar *)StringValueCStr(prefix),
                     (const xmlChar *)StringValueCStr(uri)
                    );
  return self;
}

static VALUE
register_variable(VALUE self, VALUE name, VALUE value)
{
  xmlXPathContextPtr ctx;
  xmlXPathObjectPtr xmlValue;
  Data_Get_Struct(self, xmlXPathContext, ctx);

  xmlValue = xmlXPathNewCString(StringValueCStr(value));

  xmlXPathRegisterVariable(ctx,
                           (const xmlChar *)StringValueCStr(name),
                           xmlValue
                          );

  return self;
}