C++ wrappers for GTK4 (development files)

 Gtkmm is a C++ interface for the popular GUI library GTK 4, API version 4.0.
 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 development files and examples, as well as a
 gtkmm-demo program.