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The two Document Root Nodes
As you probably know, the DOM is a tree structure description of an HTML document. Each HTML element is a tree node. The root of the tree depends on the level we start drawing the page at. We can start from the <BODY> tag. Look here for an example diagram of such a tree. We can start drawing the tree even higher, at the document object level. Then, the root of the tree is the document object. Netscape 6 introduced the documentElement node, which is the only child of the document object node. We call these two object nodes as root nodes of the tree. The W3C's Document Object Model (DOM) has several dualities. One of them is the document object vs. the documentElement object. Internet Explorer does not support the document object in the DOM. All object properties are undefined in this case. Netscape 6, on the other hand, does support both of these objects. To understand the difference between the document object and the documentElement object, look who their children are. The document object's first and last child is HTML. The documentElement object's first child, on the other hand, is HEAD, and its last child is BODY. The following buttons let you find out by yourself the value of these and other properties of the document object (bottom section) as well as those of the documentElement object (top section). We always return the node's name instead of its object, whenever applicable:
  
Next: How to use the lower root node, browser-independently
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