BPMN21 — Incomming sequence flow at start event

An interesting rule (page 245):
‘A Start Event MUST NOT be a target for Sequence Flows; it MUST NOT have incoming Sequence Flows. An exception to this is when a Start Event is used in an Expanded Sub-Process and is attached to the boundary of that Sub-Process. In this case, a Sequence Flow from the higher-level Process MAY connect to that Start Event in lieu of connecting to the actual boundary of the Sub-Process.’

I never found a tool who implements this rule. On page 261 a ‘Boundary Start event’ does not exist. Only Intermediate Events are of type ‘boundary’ (interrupting/non-interrupting). Or interrupting/non-interrupting Start Events for an Event-Sub-Process (but they are not of type ‘boundary’).

-> is it ok to remove this exception?