Publish and Subscribe was a document linking model introduced by Apple Inc. in System 7. It extended the existing cut and paste editing model with a notification system; "subscribers" could include parts of "published" documents within themselves, and changes to the original published document would be noticed and updated by the subscribers. To the user the system was very similar to cut and paste in concept; material would be selected from the source document and published, creating a clipping file, then placed into the subscriber by selecting that clipping file and positioning it inside the document.