CK Editor deletes code it does not understand

[Philip_1995]

Steps to reproduce

1. Switch code edit mode
2. Type some html that you can not generate with ckeditor e.g html 5 video player
3. switch back/submit form

Expected result

A page with a video clip

Actual result

a p tag with the message that would showing the message if browser does not support the html 5 player

Other details (browser, OS, CKEditor version, installed plugins)

This is not limited to new html 5 tags anything that ck editor does not understand will get removed/changed e.g. bootstrap classes

[Tade0]

This is by design and done by the Advanced Content Filter: ​http://docs.ckeditor.com/#!/guide/dev_acf