What else do we need to be effective at signing XML?
Something like XFDL's Signature Filters

Why sign only portions of a form?

Some forms carry non-presentation elements 'Views' for other apps (database, workflow) Some computes must remain active Separate page for data layer Other XFDL pages can show multiple views Some forms require multiple signatures Some forms require a user to only sign a portion of the form, such as 'Office Use Only' section or sections for successive signers in a workflow. Additional documents enclosed in form do not have an identity until created