An attack by 'Stinians in Gaza into Israel: Israel can attack Gaza.
Rocket attacks by Hezbollah, et al, from Syria into Israel, Israel can attack into Syria.
A rocket attack by Israel into Syria that kills Iranians, Iran can rocket attack Israel from Syria. That would be a "measured" response by Iran that would not "widen" the war. We want narrow, we don't want wide. Death to wide.
A rocket attack by Iran from Iran into Israel, not allowed. Violates No Wide rule.