The compiler accepts constraints such as

Person( fullName contains 'Jr' )  // should be fullName.contains('Jr')

Interestingly, MVEL evaluates it as the string operation "contains", but
once the constraint is jitted it is again evaluated as a collection operator.

That is, a rule such as:

  when
    $s : String( this contains "foo" ) 
  then

with inputs "foo1" .. "fooN" effectively fires an unpredictable number of times before starting to fail silently