diff --git a/src/std-traits/solution.md b/src/std-traits/solution.md
index b4a4c92cd998..a47a2c412645 100644
--- a/src/std-traits/solution.md
+++ b/src/std-traits/solution.md
@@ -3,3 +3,21 @@
 ```rust,editable
 {{#include exercise.rs:solution}}
 ```
+
+- **Wrapper Pattern:** `RotDecoder` wraps another reader `R`.
+- **Delegation:** The `read` implementation first calls `self.input.read(buf)`
+  to read data into the buffer. This is essential; we need raw data before we
+  can transform it.
+- **In-place Mutation:** After reading, the code iterates over the populated
+  part of the buffer (`buf[..size]`) and modifies the bytes in place.
+- **Error Handling:** The `?` operator is used to check the result of
+  `self.input.read`. If it fails, the error is immediately returned.
+
+<details>
+
+- Mention that `rot` is a simple Caesar cipher.
+- Chaining two ROT13 instances (rotations by 13) results in a rotation by 26,
+  which wraps around to the original text (for English alphabets). This property
+  is why ROT13 is its own inverse.
+
+</details>