This plugin requires the struct plugin which has to be installed first.
The idea of “?structat=timestamp” parameter is displaying aggregated data from struct's page schemas, as they were in a concrete moment of time. For example, imagine that you created a page: “A” with data “d.v1” at timestamp: “t1”. Then you updated the data to “d.v2” at timestamp: “t2”. Imagine that you have another page “B” with the struct table that aggregates the data from “A”. When you will visit this page, normally you will see the “d.v2” there (even when you visiting the historic versions of page older than “t1”). But when you will visit the page with the parameter: “?structat=t1”, you will see the “d.v1” in this aggregation.