Compatible Versus Incompatible Libraries

We probably need to change a library over time.

A new library version is said to be compatible with an existing library version if all of the following conditions hold true:

The semantics of each function in the library remain unchanged.
- All functions continue to produce same effect on global variables and returned arguments.
- All functions continue to return the same result values.
- Performance improvements and bug fixes (perhaps resulting in closer conformance to specified behavior) are compatible changes.
No function in the library API is removed.
New functions can be added.
The structures exported (i.e. allocated within and returned) by each function remain unchanged.
Possible exception: new items may be added to the end of the existing structure

If any of these conditions is violated, then the new library version is incompatible with the previous version.