diff --git a/library/alloc/src/collections/binary_heap/mod.rs b/library/alloc/src/collections/binary_heap/mod.rs
index b0ec70ad565..d0a87e3fb9f 100644
--- a/library/alloc/src/collections/binary_heap/mod.rs
+++ b/library/alloc/src/collections/binary_heap/mod.rs
@@ -1470,6 +1470,13 @@ impl<T> FusedIterator for IntoIter<T> {}
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<T> Default for IntoIter<T> {
+    /// Creates an empty `binary_heap::IntoIter`.
+    ///
+    /// ```
+    /// # use std::collections::binary_heap;
+    /// let iter: binary_heap::IntoIter<u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         IntoIter { iter: Default::default() }
     }
diff --git a/library/alloc/src/collections/btree/map.rs b/library/alloc/src/collections/btree/map.rs
index c1e8a84969a..8c8a459fec9 100644
--- a/library/alloc/src/collections/btree/map.rs
+++ b/library/alloc/src/collections/btree/map.rs
@@ -364,6 +364,13 @@ impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for Iter<'_, K, V> {
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<'a, K: 'a, V: 'a> Default for Iter<'a, K, V> {
+    /// Creates an empty `btree_map::Iter`.
+    ///
+    /// ```
+    /// # use std::collections::btree_map;
+    /// let iter: btree_map::Iter<'_, u8, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         Iter { range: Default::default(), length: 0 }
     }
@@ -395,6 +402,13 @@ impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for IterMut<'_, K, V> {
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<'a, K: 'a, V: 'a> Default for IterMut<'a, K, V> {
+    /// Creates an empty `btree_map::IterMut`.
+    ///
+    /// ```
+    /// # use std::collections::btree_map;
+    /// let iter: btree_map::IterMut<'_, u8, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         IterMut { range: Default::default(), length: 0, _marker: PhantomData {} }
     }
@@ -437,6 +451,13 @@ impl<K: Debug, V: Debug, A: Allocator + Clone> Debug for IntoIter<K, V, A> {
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<K, V> Default for IntoIter<K, V> {
+    /// Creates an empty `btree_map::IntoIter`.
+    ///
+    /// ```
+    /// # use std::collections::btree_map;
+    /// let iter: btree_map::IntoIter<u8, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         IntoIter { range: Default::default(), length: 0, alloc: Global }
     }
@@ -1791,6 +1812,13 @@ impl<K, V> Clone for Keys<'_, K, V> {
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<K, V> Default for Keys<'_, K, V> {
+    /// Creates an empty `btree_map::Keys`.
+    ///
+    /// ```
+    /// # use std::collections::btree_map;
+    /// let iter: btree_map::Keys<'_, u8, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         Keys { inner: Default::default() }
     }
@@ -1839,6 +1867,13 @@ impl<K, V> Clone for Values<'_, K, V> {
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<K, V> Default for Values<'_, K, V> {
+    /// Creates an empty `btree_map::Values`.
+    ///
+    /// ```
+    /// # use std::collections::btree_map;
+    /// let iter: btree_map::Values<'_, u8, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         Values { inner: Default::default() }
     }
@@ -1982,6 +2017,13 @@ impl<'a, K, V> Iterator for Range<'a, K, V> {
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<K, V> Default for Range<'_, K, V> {
+    /// Creates an empty `btree_map::Range`.
+    ///
+    /// ```
+    /// # use std::collections::btree_map;
+    /// let iter: btree_map::Range<'_, u8, u8> = Default::default();
+    /// assert_eq!(iter.count(), 0);
+    /// ```
     fn default() -> Self {
         Range { inner: Default::default() }
     }
@@ -2065,6 +2107,13 @@ impl<K, V, A: Allocator + Clone> FusedIterator for IntoKeys<K, V, A> {}
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<K, V> Default for IntoKeys<K, V> {
+    /// Creates an empty `btree_map::IntoKeys`.
+    ///
+    /// ```
+    /// # use std::collections::btree_map;
+    /// let iter: btree_map::IntoKeys<u8, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         IntoKeys { inner: Default::default() }
     }
@@ -2106,6 +2155,13 @@ impl<K, V, A: Allocator + Clone> FusedIterator for IntoValues<K, V, A> {}
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<K, V> Default for IntoValues<K, V> {
+    /// Creates an empty `btree_map::IntoValues`.
+    ///
+    /// ```
+    /// # use std::collections::btree_map;
+    /// let iter: btree_map::IntoValues<u8, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         IntoValues { inner: Default::default() }
     }
diff --git a/library/alloc/src/collections/btree/map/tests.rs b/library/alloc/src/collections/btree/map/tests.rs
index 4d011195936..76c2f27b466 100644
--- a/library/alloc/src/collections/btree/map/tests.rs
+++ b/library/alloc/src/collections/btree/map/tests.rs
@@ -563,22 +563,6 @@ fn test_iter_min_max() {
     a.check();
 }
 
-#[test]
-fn test_iters_default() {
-    let iter: Keys<'_, u8, u8> = Keys::default();
-    assert_eq!(iter.len(), 0);
-    let iter: Values<'_, u8, u8> = Values::default();
-    assert_eq!(iter.len(), 0);
-    let iter: Range<'_, u8, u8> = Range::default();
-    assert_eq!(iter.count(), 0);
-    let iter: IntoIter<u8, u8> = IntoIter::default();
-    assert_eq!(iter.len(), 0);
-    let iter: IntoKeys<u8, u8> = IntoKeys::default();
-    assert_eq!(iter.len(), 0);
-    let iter: IntoValues<u8, u8> = IntoValues::default();
-    assert_eq!(iter.len(), 0);
-}
-
 fn range_keys(map: &BTreeMap<i32, i32>, range: impl RangeBounds<i32>) -> Vec<i32> {
     Vec::from_iter(map.range(range).map(|(&k, &v)| {
         assert_eq!(k, v);
diff --git a/library/alloc/src/collections/btree/set.rs b/library/alloc/src/collections/btree/set.rs
index 897499db429..5992b814bba 100644
--- a/library/alloc/src/collections/btree/set.rs
+++ b/library/alloc/src/collections/btree/set.rs
@@ -1547,6 +1547,13 @@ impl<T, A: Allocator + Clone> Iterator for IntoIter<T, A> {
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<T> Default for Iter<'_, T> {
+    /// Creates an empty `btree_set::Iter`.
+    ///
+    /// ```
+    /// # use std::collections::btree_set;
+    /// let iter: btree_set::Iter<'_, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         Iter { iter: Default::default() }
     }
@@ -1570,6 +1577,13 @@ impl<T, A: Allocator + Clone> FusedIterator for IntoIter<T, A> {}
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<T> Default for IntoIter<T> {
+    /// Creates an empty `btree_set::IntoIter`.
+    ///
+    /// ```
+    /// # use std::collections::btree_set;
+    /// let iter: btree_set::IntoIter<u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         IntoIter { iter: Default::default() }
     }
@@ -1615,6 +1629,13 @@ impl<T> FusedIterator for Range<'_, T> {}
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<T> Default for Range<'_, T> {
+    /// Creates an empty `btree_set::Range`.
+    ///
+    /// ```
+    /// # use std::collections::btree_set;
+    /// let iter: btree_set::Range<'_, u8> = Default::default();
+    /// assert_eq!(iter.count(), 0);
+    /// ```
     fn default() -> Self {
         Range { iter: Default::default() }
     }
diff --git a/library/alloc/src/collections/linked_list.rs b/library/alloc/src/collections/linked_list.rs
index dae7fc48b1f..080a4a14eda 100644
--- a/library/alloc/src/collections/linked_list.rs
+++ b/library/alloc/src/collections/linked_list.rs
@@ -1077,6 +1077,13 @@ impl<T> FusedIterator for Iter<'_, T> {}
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<T> Default for Iter<'_, T> {
+    /// Creates an empty `linked_list::Iter`.
+    ///
+    /// ```
+    /// # use std::collections::linked_list;
+    /// let iter: linked_list::Iter<'_, u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         Iter { head: None, tail: None, len: 0, marker: Default::default() }
     }
@@ -1824,6 +1831,13 @@ impl<T> FusedIterator for IntoIter<T> {}
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<T> Default for IntoIter<T> {
+    /// Creates an empty `linked_list::IntoIter`.
+    ///
+    /// ```
+    /// # use std::collections::linked_list;
+    /// let iter: linked_list::IntoIter<u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         LinkedList::new().into_iter()
     }
diff --git a/library/alloc/src/collections/linked_list/tests.rs b/library/alloc/src/collections/linked_list/tests.rs
index 075c68f7241..04594d55b6a 100644
--- a/library/alloc/src/collections/linked_list/tests.rs
+++ b/library/alloc/src/collections/linked_list/tests.rs
@@ -172,12 +172,6 @@ fn test_iterator() {
     assert_eq!(it.next(), None);
 }
 
-#[test]
-fn test_default() {
-    let iter: IntoIter<u8> = Default::default();
-    assert_eq!(iter.len(), 0);
-}
-
 #[test]
 fn test_iterator_clone() {
     let mut n = LinkedList::new();
diff --git a/library/alloc/src/vec/into_iter.rs b/library/alloc/src/vec/into_iter.rs
index 2be484c3dd4..8fed4a584a3 100644
--- a/library/alloc/src/vec/into_iter.rs
+++ b/library/alloc/src/vec/into_iter.rs
@@ -349,6 +349,14 @@ unsafe impl<T, A: Allocator> TrustedLen for IntoIter<T, A> {}
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<T> Default for IntoIter<T> {
+    /// Creates an empty `vec::IntoIter`.
+    ///
+    /// ```
+    /// # use std::vec;
+    /// let iter: vec::IntoIter<u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// assert_eq!(iter.as_slice(), &[]);
+    /// ```
     fn default() -> Self {
         super::Vec::new().into_iter()
     }
diff --git a/library/alloc/tests/vec.rs b/library/alloc/tests/vec.rs
index 782b150681c..2f07c2911a5 100644
--- a/library/alloc/tests/vec.rs
+++ b/library/alloc/tests/vec.rs
@@ -1,6 +1,5 @@
 use core::alloc::{Allocator, Layout};
-use core::assert_eq;
-use core::iter::{ExactSizeIterator, IntoIterator};
+use core::iter::IntoIterator;
 use core::ptr::NonNull;
 use std::alloc::System;
 use std::assert_matches::assert_matches;
@@ -1036,13 +1035,6 @@ fn test_into_iter_clone() {
     assert_eq!(it.next(), None);
 }
 
-#[test]
-fn test_into_iter_default() {
-    let iter: IntoIter<u8> = Default::default();
-    assert_eq!(iter.len(), 0);
-    assert_eq!(iter.as_slice(), &[]);
-}
-
 #[test]
 fn test_into_iter_leak() {
     static mut DROPS: i32 = 0;
diff --git a/library/core/src/iter/adapters/chain.rs b/library/core/src/iter/adapters/chain.rs
index 21fc3bc6f6f..0f5e3718408 100644
--- a/library/core/src/iter/adapters/chain.rs
+++ b/library/core/src/iter/adapters/chain.rs
@@ -288,6 +288,21 @@ where
     A: Iterator + Default,
     B: Iterator + Default,
 {
+    /// Creates a `Chain` from the default values for `A` and `B`.
+    ///
+    /// ```
+    /// # use core::iter::Chain;
+    /// # use core::slice;
+    /// # use std::collections::{btree_set, BTreeSet};
+    /// # use std::mem;
+    /// struct Foo<'a>(Chain<slice::Iter<'a, u8>, btree_set::Iter<'a, u8>>);
+    ///
+    /// let set = BTreeSet::<u8>::new();
+    /// let slice: &[u8] = &[];
+    /// let mut foo = Foo(slice.iter().chain(set.iter()));
+    ///
+    /// // take requires `Default`
+    /// let _: Chain<_, _> = mem::take(&mut foo.0);
     fn default() -> Self {
         Chain::new(Default::default(), Default::default())
     }
diff --git a/library/core/src/iter/adapters/cloned.rs b/library/core/src/iter/adapters/cloned.rs
index d22a6e721f5..b9e2700860c 100644
--- a/library/core/src/iter/adapters/cloned.rs
+++ b/library/core/src/iter/adapters/cloned.rs
@@ -160,6 +160,13 @@ where
     I: Default + Iterator<Item = &'a T>,
     T: Clone,
 {
+    /// Creates a `Cloned` iterator from the default value of `I`
+    /// ```
+    /// # use core::slice;
+    /// # use core::iter::Cloned;
+    /// let iter: Cloned<slice::Iter<'_, u8>> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         Self::new(Default::default())
     }
diff --git a/library/core/src/iter/adapters/copied.rs b/library/core/src/iter/adapters/copied.rs
index d5e579834ee..0aa466e37a2 100644
--- a/library/core/src/iter/adapters/copied.rs
+++ b/library/core/src/iter/adapters/copied.rs
@@ -247,6 +247,13 @@ where
     I: Default + Iterator<Item = &'a T>,
     T: Copy,
 {
+    /// Creates a `Copied` iterator from the default value of `I`
+    /// ```
+    /// # use core::slice;
+    /// # use core::iter::Copied;
+    /// let iter: Copied<slice::Iter<'_, u8>> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         Self::new(Default::default())
     }
diff --git a/library/core/src/iter/adapters/enumerate.rs b/library/core/src/iter/adapters/enumerate.rs
index 0b44139a83b..5b0025cb984 100644
--- a/library/core/src/iter/adapters/enumerate.rs
+++ b/library/core/src/iter/adapters/enumerate.rs
@@ -270,6 +270,13 @@ impl<I> Default for Enumerate<I>
 where
     I: Iterator + Default,
 {
+    /// Creates an `Enumerate` iterator from the default value of `I`
+    /// ```
+    /// # use core::slice;
+    /// # use std::iter::Enumerate;
+    /// let iter: Enumerate<slice::Iter<'_, u8>> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         Enumerate::new(Default::default())
     }
diff --git a/library/core/src/iter/adapters/flatten.rs b/library/core/src/iter/adapters/flatten.rs
index c0a347a7c1d..cb68c807bf5 100644
--- a/library/core/src/iter/adapters/flatten.rs
+++ b/library/core/src/iter/adapters/flatten.rs
@@ -308,6 +308,14 @@ where
     I: Iterator + Default,
     <I as Iterator>::Item: IntoIterator,
 {
+    /// Creates a `Flatten` iterator from the default value of `I`.
+    ///
+    /// ```
+    /// # use core::slice;
+    /// # use std::iter::Flatten;
+    /// let iter: Flatten<slice::Iter<'_, [u8; 4]>> = Default::default();
+    /// assert_eq!(iter.count(), 0);
+    /// ```
     fn default() -> Self {
         Flatten::new(Default::default())
     }
diff --git a/library/core/src/iter/adapters/fuse.rs b/library/core/src/iter/adapters/fuse.rs
index 87275fa3951..de91c188eeb 100644
--- a/library/core/src/iter/adapters/fuse.rs
+++ b/library/core/src/iter/adapters/fuse.rs
@@ -183,6 +183,14 @@ where
 
 #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
 impl<I: Default> Default for Fuse<I> {
+    /// Creates a `Fuse` iterator from the default value of `I`.
+    ///
+    /// ```
+    /// # use core::slice;
+    /// # use std::iter::Fuse;
+    /// let iter: Fuse<slice::Iter<'_, u8>> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         Fuse { iter: Default::default() }
     }
diff --git a/library/core/src/iter/adapters/rev.rs b/library/core/src/iter/adapters/rev.rs
index 4ad75ec0ea2..0b132e13813 100644
--- a/library/core/src/iter/adapters/rev.rs
+++ b/library/core/src/iter/adapters/rev.rs
@@ -141,6 +141,13 @@ impl<I> Default for Rev<I>
 where
     I: Default + Iterator,
 {
+    /// Creates a `Rev` iterator from the default value of `I`
+    /// ```
+    /// # use core::slice;
+    /// # use core::iter::Rev;
+    /// let iter: Rev<slice::Iter<'_, u8>> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// ```
     fn default() -> Self {
         Rev::new(Default::default())
     }
diff --git a/library/core/src/slice/iter/macros.rs b/library/core/src/slice/iter/macros.rs
index 57754182c4e..a800da546b4 100644
--- a/library/core/src/slice/iter/macros.rs
+++ b/library/core/src/slice/iter/macros.rs
@@ -396,6 +396,13 @@ macro_rules! iterator {
 
         #[stable(feature = "default_iters", since = "CURRENT_RUSTC_VERSION")]
         impl<T> Default for $name<'_, T> {
+            /// Creates an empty slice iterator.
+            ///
+            /// ```
+            #[doc = concat!("# use core::slice::", stringify!($name), ";")]
+            #[doc = concat!("let iter: ", stringify!($name<'_, u8>), " = Default::default();")]
+            /// assert_eq!(iter.len(), 0);
+            /// ```
             fn default() -> Self {
                 (& $( $mut_ )? []).into_iter()
             }
diff --git a/library/core/tests/slice.rs b/library/core/tests/slice.rs
index 294de77a6b0..39559cdbb5e 100644
--- a/library/core/tests/slice.rs
+++ b/library/core/tests/slice.rs
@@ -1,10 +1,8 @@
 use core::cell::Cell;
 use core::cmp::Ordering;
-use core::iter::ExactSizeIterator;
 use core::mem::MaybeUninit;
 use core::result::Result::{Err, Ok};
-use core::slice::Iter;
-use core::{assert_eq, slice};
+use core::slice;
 
 #[test]
 fn test_position() {
@@ -226,12 +224,6 @@ fn test_iterator_count() {
     assert_eq!(iter2.count(), 3);
 }
 
-#[test]
-fn test_iterator_default() {
-    let iter: Iter<'_, u8> = Iter::default();
-    assert_eq!(iter.len(), 0);
-}
-
 #[test]
 fn test_chunks_count() {
     let v: &[i32] = &[0, 1, 2, 3, 4, 5];