StyleContext.addRegion

Adds a region to context, so posterior calls to gtk.style_context.StyleContext.get or any of the gtk_render_*() functions will make use of this new region for styling.

In the CSS file format, a #GtkTreeView defining a “row” region, would be matched by:

treeview row { ... }

Pseudo-classes are used for matching flags, so the two following rules:

treeview row:nth-child(even) { ... }
treeview row:nth-child(odd) { ... }

would apply to even and odd rows, respectively.

Region names must only contain lowercase letters and “-”, starting always with a lowercase letter.