Add copying.
diff --git a/CodeReviewComments.md b/CodeReviewComments.md
index 454806d..5b21257 100644
--- a/CodeReviewComments.md
+++ b/CodeReviewComments.md
@@ -11,6 +11,7 @@
* [gofmt](#gofmt)
* [Comment Sentences](#comment-sentences)
* [Contexts](#contexts)
+* [Copying](#copying)
* [Declaring Empty Slices](#declaring-empty-slices)
* [Doc Comments](#doc-comments)
* [Don't Panic](#dont-panic)
@@ -86,6 +87,17 @@
calls that share the same deadline, cancellation signal, credentials,
parent trace, etc.
+## Copying
+
+To avoid unexpected aliasing, be careful when copying a struct from another package.
+For example, the bytes.Buffer type contains a `[]byte` slice and, as an optimization
+for small strings, a small byte array to which the slice may refer. If you copy a `Buffer`,
+the slice in the copy may alias the array in the original, causing subsequent method
+calls to have surprising effects.
+
+In general, do not copy a value of type `T` if its methods are associated with the
+pointer type, `*T`.
+
## Declaring Empty Slices
When declaring a slice, use
