11. The method of claim 6 wherein the transformation functions specified by transformations in the sequence of transformations defined by the rule set that are to be applied to tagged message data include functions to perform cryptographic operations on a tagged portion of message data by the markup language processing device performing the transformation on behalf of the recipient computerized device.
11. The method of claim 6 wherein the transformation functions specified by transformations in the sequence of transformations defined by the rule set that are to be applied to tagged message data include functions to perform cryptographic operations on a tagged portion of message data by the markup language processing device performing the transformation on behalf of the recipient computerized device. 12. The method of claim 11 wherein the cryptographic operations include at least one of: decryption of the tagged portion of message data; encryption of the tagged portion of message data; authentication of the tagged portion of message data; signature generation on the tagged portion of message data; signature verification on the tagged message data; certificate lookup for the tagged portion of message data; certificate generation for the tagged portion of message data; and application of a secure communications protocol between the markup language processing device and a device that originated the message in response to detecting the tagged portion of message data.