Install libgtkmm-2.4-doc by entering the following commands in the terminal:
sudo apt update sudo apt install libgtkmm-2.4-doc
Description:
C++ wrappers for GTK+ (documentation)
Gtkmm is a C++ interface for the popular GUI library GTK+, with API version 2.4. Gtkmm provides a convenient interface for C++ programmers to create graphical user interfaces with GTK+'s flexible OO framework. Highlights include type safe callbacks, widgets extensible using inheritance and over 180 classes that can be freely combined to quickly create complex user interfaces. . This package contains FAQ, and reference documentation.
Homepage: http://www.gtkmm.org/
Version: 1:2.24.5-2
Section: doc