Declare a protocol for rectangle conveniences, adopted by the pre-existing category.
Change protocol to refer to protocol-conforming objects, not class names.
Forgot that ARC is not enabled on this project. Fix prematurely released object and release appropriately.
Implementation of basic set/clear spatial storage methods on sparse bit array.
Take advantages of some short cuts when count is equal to zero, or equal to length.
Fix a mistake that snuck in.
Simplify loops and avoid unnecessary object creation.
Implement missing protocol method.
Use preferred syntax avoiding too many braces/indentation.
Expand the tree if necessary when copying region from another bit array.
Implement method.