Install gnustep-gui-doc by entering the following commands in the terminal:
sudo apt update sudo apt install gnustep-gui-doc
Description:
Documentation for the GNUstep GUI Library
The GNUstep GUI Library is a powerful library of graphical user interface classes written completely in the Objective-C language; the classes are based upon the OpenStep specification, and provide the user with a traditional nextstep-like look and feel. . This package contains text, gsdoc, PDF and HTML documentation for the GNUstep GUI Library.
Homepage: http://gnustep.org
Version: 0.26.2-3
Section: universe/doc