markup language document or the method used to generate the characteristic is predefined and is not identified at all in the markup language document reference is made to fig2 which is a block diagram of an exemplary system of computers a user computer 200 has installed thereon a user agent 202 conforming to one or more markup languages a non exhaustive list of examples of user agents includes web browsers content aggregators proxy servers and search engines user computer 200 stores a markup language document 204 that includes a markup element 206 markup element 206 references a resource with a resource indicator 208 markup element 206 also includes a characteristic 210 of the resource markup language document 204 may have been generated by an authoring tool or by a human another computer 212 stores a resource 214 resource identifier 208 identifies resource 214 on computer 212 computer 212 and user computer 200 are coupled via a communication infrastructure 216 communication infrastructure 216 may include any combination of private and public networks and may optionally include parts of the internet reference is made additionally to fig3 which is a flowchart of an exemplary method for verifying the content of a resource referenced by a markup element in a markup language document the method may be implemented by a.