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Content Extraction Signatures (CES) enable selective disclosure of verifiable content, provide privacy for blinded content, and enable the signer to specify the content the document owner is allowed to extract or blind. Combined, these properties give what we call CES functionality. In this paper we describe our work in developing custom transform algorithms to expand the functionality of an XML Signature to include CES functionality in XML Signature Core Validation.We also describe a custom revocation mechanism and our implementation for non-XML content where the custom transforms are dynamically loaded demonstrating that custom signing and verification is not constrained to a 'closed system'. Through the use of dynamic loading we show that a verifier can still verify an XML Signature-compliant signature even though a custom signature was produced.