scriptorium – Wiktionary
— Read on en.m.wiktionary.org/wiki/scriptorium

Imagine a place like a library where you copy manuscripts. And part of the job falls outside of the text.

It may require you to illuminate the script: decorate or illustrate.

In the modern sense this means any decorated manuscript.

Check out the techniques, text, etc on wiki under Illuminated manuscript facts for kids at Kpedia.