Where to add valid elements?

Where can I take a look at the TinyMCE configuration valid elements in your code? I can’t see to find them in any file. I was thinking I may have to add iframe into the valid elements so it doesn’t get stripped out.

http://www.tinymce.com/wiki.php/Configuration:valid_elements

http://ww.wp.xz.cn/extend/plugins/tinymce-advanced/