BPMN21 — Link Events - Constraints and Usage not clearly documented

The Sequence Flow constraints around the usage of Link Events are not clearly expressed in the spec.

Very simply, it should express that:

• A Catch Link Event should have no incoming Sequence Flow.
• A Throw Link Event should have no outgoing Sequence Flow.

Instead the spec has several rather confusing statements (pgs 235-236) that make it hard to infer the simple behavior I described above.
Statements like:

• If the Intermediate Event is used within normal flow:
• Intermediate Events MUST be the target of a Sequence Flow.
• An Intermediate Event MUST be a source for Sequence Flow.
• An exception to this: a source Link Intermediate Event (as defined below), it is not required to have an outgoing Sequence Flow.
• A Link Intermediate Event MUST NOT be both a target and a source of a Sequence Flow.
• A Link Intermediate Event MAY be the target (target Link) or a source (source Link) of a Sequence Flow, but MUST NOT be both a target and a source.

Recommendation:

• Tighten up and simplify the constraint descriptions for Link Events.
• Refrain from introducing new terms "source" and "target", or if the new terms are needed, clearly relate them to the existing "catch" and "throw" terms.