Intro to plugin development
To get into development of IntelliJ plugins, there is a IntelliJ SDK guide. It walks the developer through several stages of developing a custom language plugin. There is a chat on Gitter that might give short answers to short questions to plugin developers: https://gitter.im/IntelliJ-Plugin-Developers/Lobby
This plugin pulled several ideas from the Markdown plugin for IntelliJ that is now part of the IntelliJ community edition. Clone the GitHub repository for IntelliJ Community and check out the Markdown plugin in particular. There is no need to make the community edition compile, just use it as a reference and look up example implementations for IntelliJ’s extension point base classes.