Ckeditor: why is formatting missing?

Question

JavaScript

I attached ckeditor to the site. All data is written to the database. After recording, all formatting is lost. This is exactly what happens if you click on the "Source" button and vice versa. The formatted image disappears.
How can you win?

Answer 1

docs.ckeditor.com/#!/guide/dev_advanced_content_filter

Answer 2

CKEditor modifies a document that it thinks is semantically incorrect. What formatting is missing?