The `typedoc-plugin-internal-external` plugin allows developers to explicitly mark TypeScript code as "Internal" or "External" using annotations in comments, providing control over how documentation is categorized in TypeDoc. It's designed for developers using TypeDoc who need more granular control over which code appears in generated documentation, particularly when the default file-based internal/external detection is insufficient. The plugin is useful for teams wanting to selectively hide internal APIs or external dependencies from their generated documentation.