I've created a plugin that extends the YAML language (amongst other things). One of the things that I ended up using was the org.jetbrains.yaml.meta.impl.YamlMetaTypeProvider (internal) that is currently part of the YAML plugin. My experience so far is that this is a very fast and pleasant API to implement/validate a specific YAML structure in my language and provides out-of-the-box key and value validations, basic completion and ... well, I don't have to tell you, you wrote it :)
My question is, are there any plans to make this API public so that I won't be surprised by a new version of IntelliJ suddenly dropping it? I can of course just copy all the classes into my plugin but I'd really rather not. Moreover, I've made some improvements to include YAML !tag identifiers in the meta-type resolving which might be a nice additional feature for it.
The entire codebase is available at: https://github.com/timmisset/omt-odt-plugin. The YAML extension is the OMT part.