Analysis of information sources in references of the Wikipedia article "Undo" in English language version.
But the most popular development for novice users in FRESS was not its capacity to accommodate multiple displays and users; it was the 'undo' feature – the feature of which van Dam is most proud (van Dam 2011). FRESS pioneered a single-level undo for both word processing and hypertext. Every edit to a file was saved in a shadow version of the data structure, which allowed for both an 'autosave' and an undo. Brown staff and students understood immediately the importance and usefulness of this feature (van Dam 1999).