Clarify that try_unwrap needs exactly one

Fixes #31950

Author: steveklabnik

src/liballoc/arc.rs

@@ -201,11 +201,12 @@ impl<T> Arc<T> {
         Arc { _ptr: unsafe { Shared::new(Box::into_raw(x)) } }
     }
 
-    /// Unwraps the contained value if the `Arc<T>` has only one strong reference.
-    /// This will succeed even if there are outstanding weak references.
+    /// Unwraps the contained value if the `Arc<T>` has exactly one strong reference.
     ///
     /// Otherwise, an `Err` is returned with the same `Arc<T>`.
     ///
+    /// This will succeed even if there are outstanding weak references.
+    ///
     /// # Examples
     ///
     /// ```

src/liballoc/rc.rs

@@ -224,11 +224,12 @@ impl<T> Rc<T> {
         }
     }
 
-    /// Unwraps the contained value if the `Rc<T>` has only one strong reference.
-    /// This will succeed even if there are outstanding weak references.
+    /// Unwraps the contained value if the `Rc<T>` has exactly one strong reference.
     ///
     /// Otherwise, an `Err` is returned with the same `Rc<T>`.
     ///
+    /// This will succeed even if there are outstanding weak references.
+    ///
     /// # Examples
     ///
     /// ```