The CK-12 resource bookmarklet allows the user to add external resources to their CK-12 library. Some websites require the CK-12 user to manually copy and paste the website's media embed code in order for the resource to be added to the CK-12 library.
Additionally, personalized content hosted on websites may require a manual copy and paste.
For a list of websites that do not require a manual copy and paste can be found here: Compatible Content Types
We will continue to update the list as we are made aware of them.