These libraries are commonly used in Gnome applications, but are not a part of
gnome-print is still somewhat experimental, but very promising. It uses libart_lgpl and works nicely with GnomeCanvas. It provides virtual output devices (called “print contexts“), so a single codebase can output to a print preview widget, to PostScript, and eventually to other printer formats. gnome-print also includes printing-related GUI elements, like a print setup dialog, and a virtual font interface (to deal with the problem that X fonts are not printable).
gnome-xml is a non-validating XML engine written by Daniel Veillard of the World
Wide Web Consortium. It can parse XML into a tree structure, and output a tree structure as XML. It’s useful for any application that needs to load and save structured data; many Gnome applications use it as a file format. This library does not depend on any of the others, not even glib — so it is tied to Gnome in name only. However, you can expect most Gnome users to have it installed, so it should not inconvenience your users if your application uses this library.
Guile is an implementation of the Scheme programming language in a library, so that any application can have an embedded Scheme interpreter. It is the official extension language of the GNU Project, and is used by several Gnome applications. Adding an extension language to your application might sound complex, but Guile makes it almost trivial. (Several Gnome applications support Perl and Python as well; it is usually easy to support several languages once you implement the first. But Guile has a special place in the Gnome developer ’s hearts.)
At press time, the Gnome hackers were putting the finishing touches on Bonobo. Bonobo is a compound document architecture in the tradition of Microsoft’s OLE; it allows you to embed charts in spreadsheets, for example. It will be used pervasively throughout Gnome; any application will be able to display MIME-typed data such as plain text, HTML, or images by asking the Gnome libraries for an appropriate Bonobo component. Look for Bonobo technology in the next major Gnome release.