Shulker Nesting
Usage
This is a very simple mod for 1.16.x that allows shulker boxes to be nested inside of each other. Warning: This can cause serious lag or crashes if abused, and as such I don't recommend installing this on servers unless you can be sure that enough RAM is allocable.
Disclaimer
This mod does not allow shulkers to be nested on vanilla servers (this check is done server-side and the box will be rejected if you try to nest it). Thankfully server admins need not worry :)
License
This mod is available under the CC0 license. Feel free to learn from it and incorporate it in your own projects.