Add criterion about which item among a set of duplicates is retained
@@ -988,7 +988,8 @@ pub trait Itertools : Iterator {
/// iterator.
///
/// The iterator is stable, returning the non-duplicate items in the order
- /// in which they occur in the adapted iterator.
+ /// in which they occur in the adapted iterator. In a set of duplicate
+ /// items, the first item encountered is the item retained.
///
/// ```
/// use itertools::Itertools;
@@ -1013,7 +1014,8 @@ pub trait Itertools : Iterator {
/// The keys are stored in a hash set in the iterator.
///
/// The iterator is stable, returning the non-duplicate items in the order
- /// in which they occur in the adapted iterator.
+ /// in which they occur in the adapted iterator. In a set of duplicate
+ /// items, the first item encountered is the item retained.
///
/// ```
/// use itertools::Itertools;
