Text folding

A folding editor is a text editor which supports text folding or code folding, a mechanism allowing the user to hide and reveal blocks of text—usually named. Typically this is done to allow the user to better picture the overall structure of a document or program.

Folding is provided by many modern text editors, and syntax-based or semantics-based folding is now a component of many software development environments.

One of the earliest folding editors was STET, an editor written for the VM/CMS operating system in 1977 by Mike Cowlishaw. STET is a text editor (for documentation, programs, etc.) which folds files on the basis of blocks of lines; any block of lines can be folded and replaced by a name line (which in turn can be part of a block which itself can then be folded).

A folding editor appeared in the occam IDE circa 1983, which was called the Inmos Transputer Development System (TDS).. The "f" editor (in list below) probably is the most intact legacy from this work.

The Macintosh computer historically had a number of source code editors that "folded" portions of code via "disclosure triangles". The UserLand Software product Frontier is a scripting environment that has this capability.

A number of text editors provide folding capability. Those that do include:

...
Wikipedia