13. A computer-based system for encoding a target document and its change history within an encapsulating document, comprising: a computer processor; computer memory which stores an encapsulation module and a focusing module; wherein the encapsulation module is configured to: receive a first version and a second version of a target document in computer memory; using the computer processor, encapsulate one of the first and second versions of the target document within an encapsulating document, the content of the one of the first and second versions being encapsulated without change to the tag or attribute values contained in the respective version of the target document; encode a change history corresponding to a difference between the first version and the second version of the target document; encapsulate the change history within the encapsulating document with a version identifier whereby a plurality of subsequent versions are encodable in the change history of the same encapsulated document with respective identifiers; and output the encapsulating document; and wherein the focusing module is configured to: receive a version identifier into computer memory; apply version differences contained within the change history to a first focused version of the target document such that, after the version differences are applied, the resulting second focused version of the target document represents the versioning point corresponding to the received version identifier; re-encode the versioning points contained within the change history relative to the second focused version of the target document; and output the re-encoded document.
13. A computer-based system for encoding a target document and its change history within an encapsulating document, comprising: a computer processor; computer memory which stores an encapsulation module and a focusing module; wherein the encapsulation module is configured to: receive a first version and a second version of a target document in computer memory; using the computer processor, encapsulate one of the first and second versions of the target document within an encapsulating document, the content of the one of the first and second versions being encapsulated without change to the tag or attribute values contained in the respective version of the target document; encode a change history corresponding to a difference between the first version and the second version of the target document; encapsulate the change history within the encapsulating document with a version identifier whereby a plurality of subsequent versions are encodable in the change history of the same encapsulated document with respective identifiers; and output the encapsulating document; and wherein the focusing module is configured to: receive a version identifier into computer memory; apply version differences contained within the change history to a first focused version of the target document such that, after the version differences are applied, the resulting second focused version of the target document represents the versioning point corresponding to the received version identifier; re-encode the versioning points contained within the change history relative to the second focused version of the target document; and output the re-encoded document. 15. The computer-based system of claim 13 , further comprising an extraction module configured to: parse and extract a version of the target document from within the encapsulating document; and output the version of the target document.