GtkSourceView is a widget that is not actually a part of the GTK+ libraries. It is an external library used to extend the Gtk::TextView widget. There is a large list of features that GtkSourceView widget adds to the text view. A list of the most notable ones follows:
- Line numbering.
- Syntax highlighting for many programming languages.
- Automatic indentation.
- Bracket matching.
- Undo/Redo support.
- Source markers for for denoting locations in the source code.
- Highlighting the current line.
If you ever used GEdit you wil recognize the following image, where you can see a sample GtkSourceView widget
The GtkSourceView library has a whole separate API documentation, which can be viewed at the GtkSourceView.sourceforge.net. If you would like to make this library available to Ruby GTK+, you'd have to compile the library yourself and write Ruby interface for it. To compile an application that uses this library, you need to add `pkg-config --cflags --libs gtksourceview-1.0` to the compile command.