I would like some confirmation about my reading of using Sea/Waterway as an available terrain feature, please. According to page 21, any of them can be chosen: "...only if compulsory or chosen by an invader for whom it is also a permitted type." My question is about "compulsory". As it is not specified, I read it means compulsory equally for a defender or an invader. Is this the case? Is so, available options would be:
1. Can be chosen by an invader if it is compulsory in its list (breaking then the rule about chosing defender terrain features only?).
2. Can be chosen by an invader as per the second condition.
3. Must be chosen by a defender if compulsory in its list and can be chosen if available but not compulsory in its list.
I guess there must be something wring in option one, but can't see what exactly. Any help will be appreciated.