Checks sum block usage to heed rule jc_0121. Exceptions allowed by the rule for loop-back signals are only applied for local loops. Signal loops incorporating parenting subsystems are not taken into account. Local signal loops including Goto-From connections and thus not forming a graphical loop construct are accepted, though.
If there is only one input defined (sum of elements), it might also be negative.
A '-' mark for the first input is only allowed, if a feedback loop actually passes through that very input, rather than through another input of the same block.
Exempted from the checks are all contents linked into the model from libraries listed in the jExclLibs parameter.