Bumping MI protocol

[Bob Rossi]

Hi,

I am wondering when the MI protocol gets bumped. Besides an MI command
that has been changed in an incompatible way, or the actual MI output
syntax changing, does the MI version get bumped for other reasons?

For example, say a new mi command gets added to version 5. Does the mi
version then become 6 because a new command has been added? 

Or does MI5 at one major release have X MI commands available, and MI5
at another major release have Y MI commands available?

Can the conditions for bumping the MI version be enumerated?
Can this information be documented for all to easily understand?

Can a front end developer find all of the functions available to a
specific version of an MI protocol from the documentation?

Thanks,
Bob Rossi