25.12.2 Nulled and predicted symbol instances

A symbol instance cannot trigger both a MARPA_EVENT_SYMBOL_NULLED and a MARPA_EVENT_SYMBOL_PREDICTED event at the same location. This is because a symbol instance must be zero-length to trigger a MARPA_EVENT_SYMBOL_NULLED event, but only non-zero length symbols will trigger a MARPA_EVENT_SYMBOL_PREDICTED event. That is, if the symbol instance is sym@start-end, a MARPA_EVENT_SYMBOL_NULLED event can trigger only if start=end, while the MARPA_EVENT_SYMBOL_PREDICTED event can trigger only if start < end.