Annotations is a plugin to add small annotations to tiddlers or to the wiki page.
The annotations don't modify any tiddlers they target. They are purely CSS based and they are all stored in a single, user-created, tiddler and they're controlled via a Controlpanel tab.
One envisioned use case is TW demos. For example, if you publish a plugin, you can annotate it to highlight features. When the user downloads your plugin, no annotations come along of course... unless you want them to: You could feature a second set of annotated instructions to your plugin.