The History filter is displayed when you choose
the Filter pop-up menu in the Test Info pane.
The default Change Only If Unique and History Always Repeats filters are based on the History filter plug-in.
This filter enables detection of a previous occurrence of the input text. When this filter is used in a test, the test keeps track of the input text from each check, and this filter can change the result status of the check based on whether the text has been seen before or not.
When the filter allows customization in the test (one of the filter options), it has two pop-up menus: one for the result to use if the text is unique, and one for not unique.
For each, the available options are
The built-in Change Only If Unique filter only results in a change for any given input text once. If that text occurs again, even after others, it'll be treated as Unchanged.
The built-in History Always Repeats filter results in a failure if the input text has not been seen before. Checking again with the same input text will recover from this failure.
These filters output the input text.