STET

The STET text editor (short for "structured editing tool") may have been the first folding editor; its first version was written in 1977 by Mike Cowlishaw. The editor runs on the IBM VM/CMS operating system. STET was written to explore an approach to text editing that followed the principles of structured programming. It allows programs and documentation to be written 'top-down', with blocks of code or text kept to a limited size (usually less than a page). This was "a first attempt to take the structure out of the domain of languages, and into the domain of editors. In addition to conventional editing facilities, STET gives the user a third dimension: a tree structure that may be traversed using Program Function Keys much as scrolling is normally implemented" Principles The editor, like many text editors, is a full-screen editor; a window into the file being edited is displayed and the lines displayed can be edited directly on-screen by insertions, deletions, or overtyping. Editing is also effected by pressing programmable action keys or by typing in commands. Commands are either 'top-line commands' (entered in a command entry area on the top line of the screen) or 'line commands' (entered in a 4-character command entry field adjacent to each displayed line of text).