'Pasting externally created source code does not work properly

Sorry if the grammar is wrong as I am using a machine translation.

I can't get the externally created source code to work when pasted into the source tab.

https://ckeditor.com/docs/ckeditor5/latest/features/source-editing.html I would like to use the Editor in the Demo on the above page, what plugin should I use? The Editor on this page works fine.

I used CKEditor 5 online builder and enabled all features except Premium, but it was not the same as the Demo.

Thank you in advance for your help.

ckeditor ckeditor5

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