Carry over: Cross Version Compatibility Approach

[bubbva]

As the work on v3.2 wound down, the TC decided to move this work item to v3.3. Copying here from our older wiki

Discussion on mandatory items in new versions of the spec which may contain new items that will break existing implementations, for example implementing a new mandatory item when it did not previously exist or requiring a mandatory attribute when something created in an previous version does not have the mandatory item. Hamish C & Tim H temporary owners.

[bubbva]

Tim & Hamish were previously assigned, assignment may no longer be accurate.