How IE's and Firefox's XML DOM parsers deal with whitespace text nodes

[Water Cooler v2]

Can someone please explain this section of this tutorial me?

http://www.w3schools.com/dom/dom_mozilla_vs_ie.asp

The relevant text I do not understand is:

"Internet Explorer, when using node.childNodes[], will NOT contain
these white-space nodes. In Mozilla, those nodes will be in the
array."

and

"Internet Explorer will skip the white-space text nodes that are
generated between nodes (e.g. new line characters), while Mozilla will
not. So, in the example above, Mozilla browsers will alert 9 child
nodes, while Internet Explorer will alert 4."

I checked the said file: http://www.w3schools.com/dom/books.xml

In both, Firefox 2.0 as well as IE 6.0, it had only 4 <bookelements.