1. A document verification system comprising digital data processors programmed to provide: an interface configured to receive electronic document runs at a presentment stage from document generation systems in excess of 500,000 documents; a normalisation component configured to transfer each document to an instance in a mark-up language taxonomy with one instance per document; a verification engine configured to perform per-document checking by checking each document instance including semantic checking using granular semantic rules within groups of items of document data, wherein the verification engine is configured to store document instances in a relational database and to set a state including a rejected state, and to remove document instances if errors are detected; a rule server configured to maintain current data item contents of each group and to maintain verification rules for execution for said semantic checking within each group; and a feedback component arranged to provide per-document error feedback arising from operation of the verification engine, wherein the feedback component is arranged to provide feedback without affecting operation of a system which generates the documents.