UML23 — Clarify that input pins do not accept more tokens than their actions can immediately consume

Clarify that input pins do not accept more tokens than their actions can immediately consume

The Activities, (12.3.2) Action, Semantics, item 1, says
The object flow prerequisite is satisfied when all of the input pins are offered all necessary tokens and accept them all at once, precluding them from being consumed by any other actions. This ensures that multiple action executions competing for tokens do not accept only some of the tokens they need to begin, causing deadlock as each execution waits for tokens that are already taken by others.
The "necessary tokens" in the first sentence above are the ones needed to execute the actions (meeting the minimum multiplicity), but should include any additional ones offered up the maximum multiplicity. Only these are accepted by the input pins, then immediately consumed by the action. The second sentence gives the motivation, which is to avoid having tokens in input pins that are not immediately consumed. This would prevent those tokens from being used to execute other actions, potentially creating deadlock or starvation. Deadlock is discussed more in issue 7221 of the UML 2.0 FTF report (http://doc.omg.org/ptc/04-10-01).