Generally speaking, in Open Source, the editor's source code and its modifications must remain accessible under the same Open Source license terms, and you must keep the copyright notices in each file intact and not delete the LICENSE.md file located in the CKEditor 4 and CKEditor 5 installation folders.
- CKEditor 4 is licensed under the terms of any of the following licenses at your choice: GPL, LGPL and MPL.
- CKEditor 5 is licensed under the terms of GPL 2+.
For more information on license requirements visit Open Source.
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