This offers three distinct modes with the first offering just what you'd expect from a drawing program with uniform line width and colour, while the second lets you draw with fully customizable gradients. Effectively this lets you draw with a picture or pictures, dragging out the vector shape or shapes along the length of the path. An obvious use is for creating picture borders with Expression's Strokes panel offering a range of repeating strokes such as footprints and chains for just this purpose. The technology is useful for much more than just an occasional eye-catching effect however. With its selection of pen strokes, for example, you can create a drawing that looks like a true work of impressionistic art with just a few strokes.
Expression offers a range of object-based and artistic brushes.
Of course you can do the same with a bitmap program like Painter but this is where the vector nature of the Expression approach really comes into its own - everything about your drawing remains completely editable. Select a stroke with the Select tool and you can immediately reposition or resize it, or choose another brush effect in the Strokes panel to produce an entirely different look. Select it with the Node tool and you can edit the shape of the brush path. The level of control leaves bitmap applications gasping. Expression 1 established the concept and the major benefits of vector brushes, but of course in the last few years other packages have picked up on the idea.