When a NetNewsWire user chooses Send to Weblog or a similar send-to-app command, NetNewsWire (usually) sends the article to the app using the External Weblog Editor Interface.

The interface defines a single Apple event that any application can handle, so that it’s easy to send articles from NetNewsWire to the app.

Some apps that support this interface: MarsEdit, Pukka, Delibar, Postr, and Webnote.