add comments

Change-Id: I2e9cea8d39c1d1e9df9ef7e8172060400b596dae

src/internal/bytealg/bytealg.go

@@ -112,6 +112,7 @@ func LastIndexRabinKarp[T string | []byte](s, sep T) int {
 }
 
 // MakeNoZero makes a slice of length n and capacity of at least n Bytes
-// without zeroing the bytes. It is the caller's responsibility to
-// ensure uninitialized bytes do not leak to the end user.
+// without zeroing the bytes (including the bytes between len and cap).
+// It is the caller's responsibility to ensure uninitialized bytes
+// do not leak to the end user.
 func MakeNoZero(n int) []byte

src/strings/builder.go

@@ -15,7 +15,11 @@ import (
 // Do not copy a non-zero Builder.
 type Builder struct {
 	addr *Builder // of receiver, to detect copies by value
-	buf  []byte
+
+	// External users should never get direct access to this buffer, since
+	// the slice at some point will be converted to a string using unsafe, also
+	// data between len(buf) and cap(buf) might be uninitialized.
+	buf []byte
 }
 
 // noescape hides a pointer from escape analysis. It is the identity function