Plugins are ways of adding new languages or formatting rules to Prettier. Prettier’s own implementations of all languages are expressed using the plugin API.

If it's dangerous, note it in the class/method Javadocs, don't just blindly slam the door shut.

— extensibility by adding new features and services through management of groups of DOI names,

Yes, using custom tags. Example in Python, making the !join tag join strings in an array:

For pluggability, an endpoint is split into a Protocol and an Adapter part. This separates generic logic from environment-dependent code.

Note how a handful of default steps lead into six standardized termini, allowing to plug protocols into different adapters. Imagine replacing your self-written API adapter with a canonical JSON-API adapter, for example.

Configurable syntax! You can add new rules and even replace existing ones.

Community-written plugins and other packages on npm.

With the new plugin based architectue, the library has really small core. Everything else is built around as a plugin.