PseudoState - WFR1 - In activity models, transitions incoming to (and outgoing from) join and fork pseudo states have as ...

[PseudoState - WFR1] - In activity models, transitions incoming to (and outgoing from) join and fork pseudo states have as sources (targets) any state vertex.  That is, joins and forks are syntactically not restricted to be used in combination with composite states, as is the case in state machines.