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.
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. 34. The computer program product of claim 21 , wherein evaluating the rule based on data describing past accesses of other ones of the plurality of document portions comprises evaluating the rule based on data describing past accesses of other ones of the plurality of document portions and further based on information regarding the request to access the document portion.