GTK+ and GNOME have gradually become platform independent. In spite of this, the primary working environment for this book is Unix. When there is a difference among Unix systems, this book leans toward a GNU system with a Linux kernel ( otherwise known as GNU/Linux or just Linux). In general, this book tries to avoid operating system dependencies, but in the interest of space and clarity, it leans toward the GNU platform because it has the overwhelming majority of GNOME installations.