12. The system of claim 11 wherein versioning information of a vNode comprises at least one of a start date corresponding to a check-in date of a version of the structured document in which the vNode is first detected, and an end date corresponding to a check-in date of another version of the structured document in which the vNode no longer exists in the structured document.
12. The system of claim 11 wherein versioning information of a vNode comprises at least one of a start date corresponding to a check-in date of a version of the structured document in which the vNode is first detected, and an end date corresponding to a check-in date of another version of the structured document in which the vNode no longer exists in the structured document. 13. The system of claim 12 wherein the versioned function is a “document-at-date” function and the at least one argument of the versioned function is a “date-point” argument that specifies a specific date, and wherein the identified version of the structured document is a version that exists on the specific date, and that includes an object represented by a vNode satisfying the query.