Control used to automatically preserve properties on a page. By calling PreserveProperty you're instructing this control to persist and then restore the value of the specified property or field of a control and have it automatically restored on the next page access.

The difference of this mechanism is that it works with ViewState off, and automatically reassigns persisted values back to the controls they belong to without any extra code. It greatly simplifies persisting values like IDs or some ViewState based values without having to use Viewstate on a page.