FUTURE

*
- use === and !== instead of == and !=
- force type conversion of input arguments in public API?
- use array push rather than string concatentation to improve performance?
- use Object.create instead of pv.extend, if available

data/?
- AJAX helper? or refer to jQuery

data/Scale.js
- allow customization of data ticks (e.g., "3 months", "5 minutes")
- greedily convert range to the expected type (for colors?)
- ignore undefined values when computing min/max for domains

mark/Mark.js
- event handlers should be inherited?
- antialias doesn't always work as expected; requires pixel rounding?
- allow mixin rather than single inheritance?
- linear and radial gradient fills
- pattern fills
- drop shadows, blurring, other graphical effects?
- animation
- faster incremental rendering (detect properties)
- remove first, last, cousin, sibling methods?
- dot-dash strokes using stroke-dasharray

mark/Bar.js
- rounded corners

mark/Line.js
- support fillStyle on segmented lines
- spline interpolation
- arrows (markers)?

mark/Label.js
- text metrics API for smart label placement

mark/Area.js
- spline interpolation

mark/Area.Radial.js
mark/Line.Radial.js
mark/Bar.Radial.js

mark/Image.js
- scale / tile / center / fill / preserveAspectRatio

physics/LinkConstraint.js
- should support an alpha parameter, like pv.Constraint.position

layout/Tree.js
- allow depth and breadth offset to be computed automatically

layout/Force.js
- smarter default rest length / charge force constant

behavior/Pan.js
- custom bounds
- lock one axis

behavior/Point.js
- compute true distance from mouse to perimeter (e.g., wedge)