18. The non-transient computer-readable medium of claim 14 , wherein the second selective digest is generated by recursively digesting the one or more invariant content items.
14. A non-transient machine-readable medium having instructions encoded thereon that, when executed by a processor, causes an electronic document validation process to be carried out, the process comprising: receiving, by an electronic document reader, an electronic document that includes (a) a plurality of content items, (b) a set of rules that defines a set of allowed operations which are authorized to be performed on the plurality of content items included in the electronic document, and (c) a first selective digest generated by a document author; identifying, by the processor, one or more invariant content items from amongst the plurality of content items, wherein the invariant content items remain unchanged when the set of allowed operations are performed on the plurality of content items included in the electronic document; generating, by the processor, a second selective digest of the one or more invariant content items; performing, by the processor, a comparison of the first selective digest generated by the document author and the second selective digest generated by the processor, wherein the comparison results in validation information; disabling, by the electronic document reader, the allowed operations when the comparison of the first and second selective digests indicates that operations have been performed on the electronic document which are not allowed under the set of rules; and saving, on a computer readable storage device, a version of the electronic document that includes the set of rules and the validation information.