The second set of elements are for applications where trust must be established in the identifier authority providing the XRD. These elements are OPTIONAL for generic authority resolution (section 9), but may be REQUIRED for specific types of trusted authority resolution (section 10) and CanonicalID verification (section 14.3). 二番目の要素セットは XRD を提供する identifier authority で信頼が確立されていなければならないアプリケーションの為