Hi,
I guess you mean you pasted the markup from the moottools example into an instance of the Html content feature using the source view.
In theory (after looking at the files in the mootools demo), that would work if you added the js to the master page and pasted the html from inside the <body> of the demo example it should work.
The problem is if you include that demo.js file in the layout.master it will be present in every page using that skin and therefore it would cause errors because the html elements that script is expecting only exists in the one page.
I don't know much about mootools but with jQuery you can select elements by css class names so it would be better to have some specific class names you use to mark an accordion, then create your own js to select the elements with the class name and create the accordion. That way you could use an accordion on any page just by marking it up correctly and there would be no errors because its not expecting elements with a particular id. If there are no elements with the designated css class then it would do nothing.
I used a similar approach to make it possible to use YUI tabs from within content as shown here.
To me its quite different to use js widgets in development of features using server side code to wire everything up and another thing entirely to make widgets creatable inside the content editor. I've done a lot of work wrapping up the YUI stuff in .NET Controls to make it easy to use them in development of features, but so far I've only wired up the tabs as something that can be used easily in the content editor, but I would like to do more. I think it would be very useful to be able to create accordions within the content by merely assigning a class name.
Best,
Joe