core::iter::repeat_with: document DoubleEndedIterator behavior

src/libcore/iter/sources.rs

@@ -158,6 +158,12 @@ unsafe impl<A, F: FnMut() -> A> TrustedLen for RepeatWith<F> {}
 ///
 /// [`repeat`]: fn.repeat.html
 ///
+/// An iterator produced by `repeat_with()` is a `DoubleEndedIterator`.
+/// It is important to not that reversing `repeat_with(f)` will produce
+/// the exact same sequence as the non-reversed iterator. In other words,
+/// `repeat_with(f).rev().collect::<Vec<_>>()` is equivalent to
+/// `repeat_with(f).collect::<Vec<_>>()`.
+///
 /// # Examples
 ///
 /// Basic usage: