This is related to http://tracker.zkoss.org/browse/ZK-1201 but I think yet another way should be supported:

I would like to extract interface over view models for them to implement.
I want methods in this interface be methods used as data bind and command methods.
I want to add @Command and @NotifyChange on the methods on the interface without the need of repeating them in the View Model class.
this does not work - ZK probably only reads annotations from the View Model class itself.

My example:
interface VMContract {

SkillSupport getSkillSupport();

@Command
@NotifyChange("skillSupport")
void editSkill(@BindingParam("skill") Skill skill);

@Command
@NotifyChange("skillSupport")
void confirmEdit();
}

and I want VM to be able to declare:

@Override
public SkillSupport getSkillSupport()

{ return skillSupport; }

@Override
public void editSkill(@BindingParam("skill") Skill skill)

{ skillSupport.editSkill(skill); }

@Override
public void confirmEdit()

{ skillSupport.confirmEdit(); }

without any of those @Command and @NotifyChange

I don't want to add @NotifyChange(superclass=true) on each of the methods, acceptable solution would be to configure it on a VM class level.