CKEditor Stripping button tags

[Callum MacGregor]

I'm trying to add an accordion as a custom button to ckeditor using this code example: http://www.w3schools.com/howto/howto_js_accordion.asp

I've added the CSS and JS appropriately but the button tags are stripped out when I save it. I've added the 'accordion' and 'panel' classes to CKEditor's list of allowed classes in the admincp but that didn't work.

Any ideas?