How does Myspace create it's pages to allow users to apply code changes, what languages and techniques?

IMPORTANT NOTE: I am NOT trying to mimic myspace or create any page even related to myspace what so ever, I'm only interested in the knowledge in it's entirety.

I think it's very interesting how websites allow users to enter code and change the way a page looks. I would love to know what techniques and languages are used to accomplish this.

Thank you very much!

It's pretty easy to do. In fact, most sites do allow it if they aren't secured properly.

If you use MySpace, you know that there are no designated places for style changes. (At least there wasn't years ago when I tried MySpace.)

You just type <style> CSS code </style> in any one of the text boxes, and the style would be used on your page.

This is the way it works on any website if you don't tell it otherwise. However, this opens up security holes. Also, most sites don't want you to change the layout.

Most sites just strip out all HTML, CSS, Javascript, ect. from any user input. (At least they should.)

MySpace does strip out anything that could cause security problems but they allow the <style> tag. That's all there is to it.