3rd:Scintilla Editor Control
Notice Since Visual Prolog 7.4 the scintilla editor is part of Visual Prolog.
Scintilla (http://www.scintilla.org/) is a text editor with many features such as tooltips, autocompletion, folding, syntax coloring etc...
This custom control wraps the scintilla dll to let you use it to replace the PDC's edit control. It has many more features and let you define your own keyword list, own color set, font, underline, folding etc..
The included project shows how to perform a folding/unfolding as well as syntax coloring for different list of keywords and indentation control. The scintilla control has many more features that can be used and changed at runtime.
Also see changes in Discussion forum: custom control : scintilla editor