def condition(proc)
      return unless block_given?
      @template.add_node Nodes::Condition.new(proc, sub_compile(nil, true) { yield })
    end
def condition(proc)
      return unless block_given?
      @template.add_node Nodes::Condition.new(proc, sub_compile(nil, true) { yield })
    end
Provide a conditionnal block

 condition(->(u) { u.is_a?(Admin) }) do
   attributes :secret
 end