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.
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).
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: