It's a small, jij-able API that allows creation and parsing placeholders within strings and Minecraft Text Components.
Placeholders use simple format of %modid:type% or %modid:type/data%.
It also includes simple, general usage text format indented for simplifying user input in configs/chats/etc.
For information about usage (for developers and users) you can check official docs at https://placeholders.pb4.eu/!