This plugins allows you to create a "Discoveries Inventory" where your players can access information about specific regions, people, monsters they've encountered. Codex is a plugin that adds a little bit of RPG experience to your Minecraft server, by providing context and lore to the player.
You can create any "Discovery" you want, players will unlock them by entering regions for the first time, talking to NPCs, killing monsters, and you can even unlock discoveries to players by using a console command! So the plugin allows you to create discoveries associated with aspects of other plugins.
For example, you can create a Region Discovery which will be unlocked if the player arrives at certain city. The player has the possibility to access the Codex by using /codex and read the lore of this city which provides more information.