2022
Chris McDonough - Rants and Asides: Failure of NixOS #32 Using An Overlay To Change The Source of a nixpkgs Pkg Drunk 0:00 of 21:10
    https://www.youtube.com/watch?v=0B4RjRk65_Q
    https://github.com/mcdonc/.nixconfig/blob/master/videos/overlays/script.rst
2020
Ringer - Nixpkgs - Overlays 0:00 of 6:22
    https://www.youtube.com/watch?v=dGAL3gMXvug
    ! need to look
2017
Nixcon - Nixpkgs Overlays – A place for all excluded packages by Nicolas B. Pierron (NixCon 2017) 0:00 of 42:54
    https://www.youtube.com/watch?v=W85mF1zWA2o
    http://nbp.github.io/slides/NixCon/2017.NixpkgsOverlays/