Re-word PR 156

Author: dtolnay

_src/container-attrs.md

@@ -70,14 +70,14 @@
   Use the untagged enum representation for this enum. See [enum representations]
   for details on this representation.
 
-  When no variant matches, the error may be uninformative which can be improved
-  with [`serde(expecting)`](#expecting).
+  When no variant matches, `untagged` does not produce an informative error but
+  this can be improved by adding an [`expecting`](#expecting) message.
 
-  In performance-critical code, checking each variant and processing the errors
-  can be slow. In these cases, it may be better to hand-implement the
-  deserialize trait for which [serde-untagged] may help.
+  In performance-critical code, the implementation approach used by `untagged`
+  can be costly. Consider implementing the Deserialize trait by hand or with the
+  help of the [`serde-untagged`] crate.
 
-  [serde-untagged]: https://docs.rs/serde-untagged
+  [`serde-untagged`]: https://docs.rs/serde-untagged
 
 - ##### `#[serde(bound = "T: MyTrait")]` {#bound}