This interface represents a signature template, which is the same as the
* desired xml signature element but some of the nodes may be empty. The empty
* entities include digest value and signature value. Empty entities are not
* allowed in a signature template when performing validation.
*
*
In some cases, the signer or vertifier can dertermine and locate the
* contents to be signed from the template by dereference the URI.
*
*
With the help of signature context, the signer or verifier specifies the
* key from the KeyInfo in the signature template.
