From Edutechwiki - Reading time: 3 min“X3DOM (pronounced X-Freedom) is an experimental open source framework and runtime to support the ongoing discussion in the Web3D and W3C communities how an integration of HTML5 and declarative 3D content could look like. It tries to fulfill the current HTML5 specification for declarative 3D content and allows including X3D elements as part of any HTML5 DOM tree.” (X3dom.org, retrieved 12:29, 25 August 2010 (UTC)).
The X3DOM (if accepted as specification which seems to be very likely) is to WebGL what SVG is to canevas. This relationship is nicely explained in the following figure found at x3dom.org

Alpha implementations work with browsers that implement WebGL (e.g. Firefox 4.0). See X3DOM for more information. Firefox 4 users will have to enable WebGL (see the Tour 3D).
We have no idea what parts of X3D will be available in HTML5. If I understand right, scripting will be done through the HTML DOM and not through the SAI. As of today, several demos running with the help of a JavaScript library exist. Fairly impressive.
No DOM scripting at the end-user level, X3D is implemented as a small javascript library.
Life source: http://x3dom.org/x3dom/example/x3dom_helloWorld.html
<!DOCTYPE html >
<html >
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
<title>Hello World</title>
<link rel="stylesheet" type="text/css" href="x3dom.css" />
<script type="text/javascript" src="x3dom.js"></script>
</head>
<body>
<h1>HTML5 Hello World</h1>
<p>
With X3DOM-namespace and lower-case element/node names. Does not work with self closing tags (e.g viewpoint and material) right now.
</p>
<x3d xmlns="http://www.x3dom.org/x3dom" showStat="false" showLog="false" x="0px" y="0px" width="400px" height="400px" altImg="helloX3D-alt.png">
<scene>
<viewpoint position='0 0 10' ></viewpoint>
<shape>
<appearance>
<material diffuseColor='0.603 0.894 0.909' ></material>
</appearance>
<box DEF='box' ></box>
</shape>
</scene>
</x3d>
</body>
</html>