Update set.rs

Author: Xylenox

library/alloc/src/collections/btree/set.rs

@@ -1309,6 +1309,8 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// Passing `Bound::Unbounded` will return a cursor pointing to the
     /// gap before the smallest element in the set.
     ///
+    /// Represents the gap at the beginning of a range with the given bound as it's lower bound.
+    ///
     /// # Examples
     ///
     /// ```
@@ -1352,6 +1354,8 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// Passing `Bound::Unbounded` will return a cursor pointing to the
     /// gap before the smallest element in the set.
     ///
+    /// Represents the gap at the beginning of a range with the given bound as it's lower bound.
+    ///
     /// # Examples
     ///
     /// ```
@@ -1395,6 +1399,8 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// Passing `Bound::Unbounded` will return a cursor pointing to the
     /// gap after the greatest element in the set.
     ///
+    /// Represents the gap at the end of a range with the given bound as it's upper bound.
+    ///
     /// # Examples
     ///
     /// ```
@@ -1438,6 +1444,8 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// Passing `Bound::Unbounded` will return a cursor pointing to the
     /// gap after the greatest element in the set.
     ///
+    /// Represents the gap at the end of a range with the given bound as it's upper bound.
+    ///
     /// # Examples
     ///
     /// ```