TYPO3 Core

When a custom CKEditor plugin is modified, if it was in the browser cache before, the old version can be loaded.

To prevent this, CKEDITOR.timestamp can be used to add a "?t=" parameter to the url of plugins JS files.
CKEDITOR.timestamp has a default value in ckeditor.js and changes with every ckeditor releases.
On TYPO3 8.7 with ckeditor 4.11.1, CKEDITOR.timestamp is "IA8E" (it is not a real timestamp).

TYPO3 should override CKEDITOR.timestamp with a custom hash.
In a ideal scenario, this hash should be recalculated every time a custom plugin is edited.
But it is not very possible.

So I suggest that this hash can be the result of a MD5 of ckeditor configuration.
Every time the configuration is changed (like when adding an external plugin), the hash will change, and the browser cache will not serve an old version of a plugin.