The getElementsByTagName method returns a NodeList collection of those elements with the tag name specified as the argument. If you use the value "*" as the argument, then a list of all elements is returned.

In the following example we first load the 'passeriformes.xml' file, which details the bird species in that order, and then create a NodeList of all the 'species' elements. The code then iterates through the collection displaying the value of each firstChild node (the text node).

XML:
<passeriformes>
   <family>
      <f_name>Alaudidae</f_name>
      <species>Woodlark</species>
      <species>Skylark</species>
      <species>Shore Lark</species>
   </family>
   <family>
      <f_name>Motacillidae</f_name>
      <species>Rock Pipit</species>
      <species>Water Pipit</species>
      <species>Yellow Wagtail</species>
   </family>
   <family>
      <f_name>Turdidae</f_name>
      <species>Robin</species>
      <species>Nightingale</species>
      <species>Blackbird</species>
   </family>
</passeriformes>

Code (JavaScript):
var xml_doc = new ActiveXObject("Microsoft.XMLDOM");
xml_doc.async = false;
xml_doc.load("passeriformes.xml");

var i, n_elems, elems = xml_doc.getElementsByTagName("species");
n_elems = elems.length;
for (i = 0; i < n_elems; i++)
   document.write(elems[i].firstChild.nodeValue + "<br>");

Output:
Woodlark
Skylark
Shore Lark
Rock Pipit
Water Pipit
Yellow Wagtail
Robin
Nightingale
Blackbird