gokogiri nodeset

I want to learn to use gokogiri, but there aren't many sample code I can find, so I'm translating a C code from http://veillard.com/XML/examples/xpath2.c

However, the problem is that it uses nodeset, and I cannot find a single gokogiri sample code using nodeset, so I'm stuck. My question has been asked and stayed at golang-nuts group for several days, without anyone knowing the answer. The following is best I can do so far. Please help me finish. Thanks.

/*

Goal:

Load a document, locate subelements with XPath, modify said elements and save the resulting document.

*/

package main

import (
	"fmt"
	"os"
	//"io/ioutil"

	"github.com/moovweb/gokogiri"
	//"github.com/moovweb/gokogiri/xpath"
)

func main() {
	// content, _ := ioutil.ReadFile("index.html")
	//doc, _ := gokogiri.ParseHtml(content)
	content := `<?xml version="1.0"?>
<?xml-stylesheet href="catalog.xsl" type="text/xsl"?>
<!DOCTYPE catalog SYSTEM "catalog.dtd">
<catalog>
   <product description="Cardigan Sweater" product_image="cardigan.jpg">
      <catalog_item gender="Men's">
         <item_number>QWZ5671</item_number>
         <price>39.95</price>
         <size description="Medium">
            <color_swatch image="red_cardigan.jpg">Red</color_swatch>
            <color_swatch image="burgundy_cardigan.jpg">Burgundy</color_swatch>
         </size>
         <size description="Large">
            <color_swatch image="red_cardigan.jpg">Red</color_swatch>
            <color_swatch image="burgundy_cardigan.jpg">Burgundy</color_swatch>
         </size>
      </catalog_item>
      <catalog_item gender="Women's">
         <item_number>RRX9856</item_number>
         <price>42.50</price>
         <size description="Small">
            <color_swatch image="red_cardigan.jpg">Red</color_swatch>
            <color_swatch image="navy_cardigan.jpg">Navy</color_swatch>
            <color_swatch image="burgundy_cardigan.jpg">Burgundy</color_swatch>
         </size>
         <size description="Medium">
            <color_swatch image="red_cardigan.jpg">Red</color_swatch>
            <color_swatch image="navy_cardigan.jpg">Navy</color_swatch>
            <color_swatch image="burgundy_cardigan.jpg">Burgundy</color_swatch>
            <color_swatch image="black_cardigan.jpg">Black</color_swatch>
         </size>
         <size description="Large">
            <color_swatch image="navy_cardigan.jpg">Navy</color_swatch>
            <color_swatch image="black_cardigan.jpg">Black</color_swatch>
         </size>
         <size description="Extra Large">
            <color_swatch image="burgundy_cardigan.jpg">Burgundy</color_swatch>
            <color_swatch image="black_cardigan.jpg">Black</color_swatch>
         </size>
      </catalog_item>
   </product>
</catalog>`
	doc, _ := gokogiri.ParseXml([]byte(content))
	defer doc.Free()

	if len(os.Args) <= 1 {
		fmt.Println(doc.String())
	} else if len(os.Args) == 3 {
		example4(os.Args[1], os.Args[2])
	} else {
		fmt.Println("Usage: lx2_xpath-search1 xpath-expr new-value")
	}
}

func example4(doc *xml.XmlDocument, xpathExpr, value string) {
	/* Create xpath evaluation context */
	xpathCtx := doc.DocXPathCtx()
	/* Evaluate xpath expression */
	xpathObj := xpathCtx.EvalXPath(xpathExpr, nil) // xpath.ResolveVariable
	/* update selected nodes */
	updateXpathNodes(xpathObj.ResultAsNodeset(), value)
}

func updateXpathNodes(??) {
  ??
}

Can someone shows me how to use the gokogiri nodeset please? (ResultAsNodeset() will return "nodes []unsafe.Pointer" etc. I have no clue how to use it)

Thanks