25. The computer program product of claim 21 , wherein the rule indicates that access to the requested document portion is denied responsive to the data describing past accesses indicating that access was provided to one or more other document portions on more occasions than access was provided to the requested document portion.
21. A computer program product for controlling access to a portion of a document, the document comprising a plurality of portions, the computer program product comprising a computer readable storage medium storing a computer program for performing a method, the method comprising: receiving a request to access the document portion; identifying a variable accessibility rule associated with the requested document portion; evaluating the rule based on data describing past accesses of other ones of the plurality of document portions; determining whether to provide access to the requested document portion responsive to the evaluation of the rule; and responding to the request based on the determination.