About Iframes and it's restriction...

What is Iframe??
Iframe or Inline Frames is an new element of html document that allow you to load html files inth and existing document.
What browser support iframe?
IE4+, Netscape6+, Firefox, Mozilla, Opera and other modern browsers all support iframes.

An External html document can be loaded into iframe without disrupting the rest of the document. Styling and Scripting in iframe can be manipulate properties in the iframe itself as original html document. The document style does not inherit from containing document.
JavaScript can be used to communicate betaween document in iframe and containing document.

Note
When you try to access properties of document that loaded into iframe, make sure that the document loaded into iframe come from same domain, else you got "permission denied".
....event it's the sub domain you still got "permission denied".

Next.. article I will show some example of scripting with iframe..