It is perhaps not critical to understand now, but those who want to take a look at what is perhaps ahead, should consider checking out E4X, or ECMAScript for XML. It has already been implemented in SpiderMonkey and Rhino, and has been standardized in ECMA-357 standard.
This is particularly attractive -- from page 11 of the E4X slides:
* Expandos make markup composition a snap!
* Just start appending extra property tiers:
var html = <html/@lt;
html.head.title = "My Page Title";
html.body.@bgcolor = "#e4e4e4";
html.body.form.@name = "myform";
html.body.form.@action = "someurl.jss";
html.body.form.@method = "post";
html.body.form.@onclick = "return somejs();";
html.body.form.input = "";
html.body.form.input.@name = "test";
* Results in this XML:
<title>My Page Title</title>
<form name="myform" action="someurl.jss"
method="post" onclick="return somejs();">
...the future is surely bright for open source, browser native, Ajax.