BPMN21 — Throughout Spec [Specification]: Define explicit separation of "modeling" vs "implementation" attributes

This is number 1 of 12 issues submitted by Bruce Silver:

Define explicit separation of "modeling" vs "implementation" attributes. The current "core" vs "extended" is nowhere close to this, since modeling needs much of the extended set. Modeling is about orchestration of "abstract" activities, abstract meaning they have a name (label), task type, perhaps markers like loop/MI/adhoc, and unique id of course, but not implementation properties. Abstract sequence flow has name, source and target refs; if conditional, the label is sufficient - you don't require a conditionExpression. Message flow or message event does not require a message attribute, timer event does not require TimeDate or TimeCycle (please rename it to Duration) attribute, error event does not require an error code attribute, etc. Those are for implementation; in modeling it's the diagram that counts, i.e. the label.