gistfile1.txt

@Command
public String tell(EntityRef sender, @CommandParam(value = "target", suggester = SUGGESTER_PLAYER) EntityRef target, String message) {
    return "sent.";
}
 
private class PlayerSuggester extends Suggester {
    @Override
    public List<EntityRef> suggest() {
        return /*all entityrefs of players*/;
    }
}