This field allows you to search for artifacts with attributes that have changed from one value to another value.
For example, to query for artifacts where a value has not been selected for an attribute, you can create a query to find all of the defect artifacts where "Operating System" has not been selected. In the same query, you can stipulate that all artifacts that have their short text fields not filled in should be displayed. To combine these two query criteria, the results will contain all artifacts which do not have the Operating System specified and the short text field not filled in.