diff --git a/book.toml b/book.toml
index 0d84c17318..5b86f6808a 100644
--- a/book.toml
+++ b/book.toml
@@ -3,6 +3,9 @@ title = "Rust By Example"
 description = "Rust by Example (RBE) is a collection of runnable examples that illustrate various Rust concepts and standard libraries."
 author = "The Rust Community"
 
+[rust]
+edition = "2021"
+
 [output.html.playpen]
 editable = true
 editor = "ace"
diff --git a/src/error/result/enter_question_mark.md b/src/error/result/enter_question_mark.md
index 8101e3efd7..ca954b1ac2 100644
--- a/src/error/result/enter_question_mark.md
+++ b/src/error/result/enter_question_mark.md
@@ -43,7 +43,7 @@ The `?` operator is now recommended, but you may still find `try!` when looking
 at older code. The same `multiply` function from the previous example
 would look like this using `try!`:
 
-```rust,editable
+```rust,editable,edition2015
 // To compile and run this example without errors, while using Cargo, change the value 
 // of the `edition` field, in the `[package]` section of the `Cargo.toml` file, to "2015".
 
diff --git a/src/fn/closures/closure_examples/iter_any.md b/src/fn/closures/closure_examples/iter_any.md
index 1fb64e9707..3c11f43c9b 100644
--- a/src/fn/closures/closure_examples/iter_any.md
+++ b/src/fn/closures/closure_examples/iter_any.md
@@ -35,7 +35,7 @@ fn main() {
     // `iter()` for arrays yields `&i32`.
     println!("2 in array1: {}", array1.iter()     .any(|&x| x == 2));
     // `into_iter()` for arrays unusually yields `&i32`.
-    println!("2 in array2: {}", array2.into_iter().any(|&x| x == 2));
+    println!("2 in array2: {}", array2.into_iter().any(| x| x == 2));
 }
 ```
 
diff --git a/src/generics/assoc_items/types.md b/src/generics/assoc_items/types.md
index 0358fcebca..dbf6d789b4 100644
--- a/src/generics/assoc_items/types.md
+++ b/src/generics/assoc_items/types.md
@@ -1,6 +1,6 @@
 # Associated types
 
-The use of "Associated types" improves the overall readability of code 
+The use of "Associated types" improves the overall readability of code
 by moving inner types locally into a trait as *output* types. Syntax
 for the `trait` definition is as follows:
 
@@ -13,7 +13,7 @@ trait Contains {
     type B;
 
     // Updated syntax to refer to these new types generically.
-    fn contains(&self, &Self::A, &Self::B) -> bool;
+    fn contains(&self, _: &Self::A, _: &Self::B) -> bool;
 }
 ```