gtk-render-extension (context cr x y width height side)

context -- a gtk-style-context object
cr -- a cairo-t context
x -- a number, coerced to a double float, with the x origin of the rectangle
y -- a number, coerced to a double float, with the y origin of the rectangle
width -- a number, coerced to a double float, with a rectangle width
height -- a number, coerced to a double float, with a rectangle height
side -- a value of the gtk-position-type enumeration where the gap is

Renders a extension as in a gtk-notebook widget tab in the rectangle defined by x, y, width, height. The side where the extension connects to is defined by side.