How to allow for embed of arbitrary script tag

A followup, if you don’t mind: after your answer, I searched on here for textarea and script, and found a reference to the opposite idea, of wanting to disallow script tags in a text editor, and @texnixe you mention one can use kirbytext filters to accomplish it.

The link you reference is dead, and I can’t find any reference to kirbytext filters. Do they still exist in the 3.5 version today?