for situations where an instrument was created or designed by an (artist) (sumably one already in the database)

examples:

• accordina https://beta.musicbrainz.org/instrument/4d4e45e0-660d-4456-89cd-47a3fa14bb7c (André Borel)
• craviola https://beta.musicbrainz.org/instrument/1eb5e0b3-4fde-482f-a7b3-6d1f69f9dd46 (Paulinho Nogueira)
• gizmo https://en.wikipedia.org/wiki/The_Gizmo (Kevin Godley and Lol Creme)
• Ernst Zacharias:
• Claviola
• Pianet
• Clavinet (https://beta.musicbrainz.org/instrument/563a9f16-e84b-409a-bda5-2e4ce09d5573)

• many keytars https://en.wikipedia.org/wiki/List_of_keytars (as well as synthesisers and moogs etc.)
• several custom instruments also.