Document minmax behaviour when several elements are equally minimum or maximum
@@ -399,6 +399,9 @@ impl<I, K, V> GroupingMap<I>
/// Groups elements from the `GroupingMap` source by key and find the maximum and minimum of
/// each group.
///
+ /// If several elements are equally maximum, the last element is picked.
+ /// If several elements are equally minimum, the first element is picked.
+ ///
/// See [.minmax_by()](../trait.Itertools.html#method.minmax) for the non-grouping version.
///
/// Differences from the non grouping version:
@@ -429,6 +432,9 @@ impl<I, K, V> GroupingMap<I>
/// Groups elements from the `GroupingMap` source by key and find the maximum and minimum of
/// each group with respect to the specified comparison function.
///
+ /// If several elements are equally maximum, the last element is picked.
+ /// If several elements are equally minimum, the first element is picked.
+ ///
/// It has the same differences from the non-grouping version as `minmax`.
///
/// Returns a `HashMap` associating the key of each group with the minimum and maximum of that group's elements.
@@ -476,6 +482,9 @@ impl<I, K, V> GroupingMap<I>
/// Groups elements from the `GroupingMap` source by key and find the elements of each group
/// that gives the minimum and maximum from the specified function.
///
+ /// If several elements are equally maximum, the last element is picked.
+ /// If several elements are equally minimum, the first element is picked.
+ ///
/// It has the same differences from the non-grouping version as `minmax`.
///
/// Returns a `HashMap` associating the key of each group with the minimum and maximum of that group's elements.
