Question

In the w3school site there are two tutorials:

HTML DOM

XML DOM

I want to know the releationship of them, since I think the HTML DOM is one kind of XML DOM.

So the methods/properties in the XML DOM can be used in HTML DOM, and the HTML DOM may own some special methods.

However, when I try to use this:

HTML:

<span id="con">xxx</span>

var a=document.createElement("a");
document.getElementById("con").appendChild(a);

It does not work in IE.

So I wonder what is the problem?

Answer 1

DOM refers to a tree you make out of XML. The tree is made up of nodes. For example:

<a x="bb">
   <b> text </b>
</a>

turns into a tree with three nodes: one for a and one for b and one for the text. The nodes contains the attributes as fields. So the a node will have a field: x="bb".

HTML is (practically) XML so you can build a DOM tree out of it. HTML is just XML with predefined elements. I.e., you can’t use whatever names you want for your elements (you can’t use <children>, <ball>,…) you can use the predefined names (a, span, div, …).

I say “practically” because HTML is usually broken XML (for example using <br> is wrong XML. you should use <br /> instead). The browsers have smart parsers that know how to overcome this broken XML and make a usuable tree out of the HTML.