setting border width

["Dafna Hirschfeld" <dafna3 gmail com>]

I couldn't find how to set a border of a widget. I don't mean the space around the widget but the border line itself.
The entry widget and the check-button come with a border line by default (the entry widget even have a little shadow).
But the TextView  has no border by default , How can I add a border?
I fond the function paint_shadow of Style, and a struct GtkBorder but I couldn't understand if this is what I need and how to use it.