Searches groups of species containing
the same value or
identical words in values
in the field selected at 'Search field' of the first query.
All duplicated occurrences are added to the hitlist - first occurrence gets '1st' added, following occurrences get 'dup' added.
The first occurrence is NOT marked, all following occurrences get marked - so you can easily perform some action on duplicates.
To mark the first occurrences as well, click on 'Mark Listed Unmark Rest' (to mark all species currently listed).