[DB-SIG] what is: backwards compatibility

[Carl Karsten]

I'm still trying to come up with a set of possible meanings for backwards
compatibility, something like

doesn't break:

any existing code
any conceivable code
reasonable code
code that conforms to any documentation found, including module code.
code that conforms to the docs bundled with the module
code that conforms to the docs found under python.org
code that conforms to pep 249

But I have a feeling I am missing something.

I think the problem is separating it from how much of it is reasonable for dbapi 
v3.

also, Anyone have a list of what dbapi v2 modules exist, and therefor need to be 
   accommodated?

Carl K