Parsing Childnode values in javascript

I have an XML

<root><example><examplevalue>exampletext</examplevalue><examplevalue>exampletext2</examplevalue</example></root>

and I have the following javscript code

            if (window.DOMParser){ // Standard browsers
                var parser = new DOMParser();
                xmlDoc = parser.parseFromString(xmlString, "text/xml");
            }
            else { // Internet Explorer
                xmlDoc = new ActiveXObject("Microsoft.XMLDOM");
                xmlDoc.async = false;
                xmlDoc.loadXML(xmlString); 
            }
            var coll=xmlDoc.getElementsByTagName("example");
            console.log(coll[0].childNodes[0].nodeValue);

The console output is

null

I would expect it to be

exampletext

Why are the childnodes not parsed correctly?
childNodes seems to be a method of class node. But the getElementByName return a HTMLCollection object. How does that work?
Thanks for any hints.