R^2
Angles
Paths
Stroking
Clipping
Shapes
Rules
Circle-ish things
General polygons
Star polygons
Regular polygons
Other special polygons
Other shapes
Arrows
Text
Images
Transformations
Rotation
Scaling
Translation
Reflection
Shears
Deformations - non-affine transforms
Combinators
Combining multiple diagrams
Spacing and envelopes
Background
Alignment
Snugging
Size
Computing size
Specifying size
Adjusting size
Visual aids for understanding the internal model