code: function xpathEval(select, context, ns) {
      var str = select;
      if (ns !== undefined) {
          if (context.node)
              str = context.node.prepare(select, ns);
      }
      //parse statement
      var expr = xpathParse(str);
      //and return value
      return expr.evaluate(context);
  }
docs: Parses and then evaluates the given XPath expression in the given input context.
  @param {String} select
  @param {ExprContext} context
  @param {Array=} ns
  @returns {Object}