A markup language processing device processes markup language messages by receiving a message containing portions of tagged data formatted in a markup language and applying a transform selection rule set to at least one tagged rule selection data portion in the message to select at least one markup language transformation to apply to the tagged pre-transform data portion within the message. The markup language processing device applies the selected markup language transformation to transform the tagged pre-transform data portion to a tagged post-transform data portion according to a transformation function and then conditionally forwards the message. The markup language processing device operates on behalf of a computerized device that is not required to process the message due to operation of the at least one markup language transformation within the markup language processing device. The markup language processing device can process XML message for security and other purposes thus offloading such processing requirement from server computer systems.