Document from_raw_parts involves ownership transfer

src/libcollections/string.rs

@@ -701,6 +701,12 @@ pub fn from_utf16_lossy(v: &[u16]) -> String {
     /// Violating these may cause problems like corrupting the allocator's
     /// internal datastructures.
     ///
+    /// The ownership of `ptr` is effectively transferred to the
+    /// `String` which may then deallocate, reallocate or change the
+    /// contents of memory pointed to by the pointer at will. Ensure
+    /// that nothing else uses the pointer after calling this
+    /// function.
+    ///
     /// # Examples
     ///
     /// Basic usage:

src/libcollections/vec.rs

@@ -348,6 +348,12 @@ pub fn with_capacity(capacity: usize) -> Vec<T> {
     /// Violating these may cause problems like corrupting the allocator's
     /// internal datastructures.
     ///
+    /// The ownership of `ptr` is effectively transferred to the
+    /// `Vec<T>` which may then deallocate, reallocate or change the
+    /// contents of memory pointed to by the pointer at will. Ensure
+    /// that nothing else uses the pointer after calling this
+    /// function.
+    ///
     /// # Examples
     ///
     /// ```