The commit reference page lacks an "Outputs" section even though it is capable of outputting both "COMMIT" and "ROLLBACK".
The attached adds this section, describes when each applies, and then incorporates the same into the main description for commit as well as the transaction section of the tutorial - which presently seems to be the main discussion area for the topic (the Concurrency Control chapter lacks a section for this introductory material).
This was noted as being needed by Tom Lane back into 2006 but it never happened.
It came up again when I was answering a question on Slack regarding "commit and chain" wondering whether the "and chain" could be made conditional (i.e., could the new transaction start aborted) on whether commit outputted "commit" or "rollback".
Its left implied that this behavior of "rollback" is standard-conforming. Please feel free to suggest/add language to the Compatibility section if this is not the case.
