Install gnome-api-docs by entering the following commands in the terminal:
sudo apt update sudo apt install gnome-api-docs
Description:
API reference documentation for the GNOME libraries
This metapackage brings all available API documentation for the libraries of the GNOME platform, as well as their important dependencies. This should be most of the documentation you need to write GNOME applications. . This documentation is best viewed within the devhelp documentation browser.
Version: 1:3.22+9
Section: universe/doc