From d3e8729a0773df492c1b28d65588cc03a72748a8 Mon Sep 17 00:00:00 2001
From: Mark Mansi <markm@cs.wisc.edu>
Date: Sat, 22 Sep 2018 13:48:55 -0500
Subject: [PATCH 1/2] Edition notes about

---
 src/SUMMARY.md                       |  1 +
 src/rust-2018/macros/at-most-once.md | 38 ++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)
 create mode 100644 src/rust-2018/macros/at-most-once.md

diff --git a/src/SUMMARY.md b/src/SUMMARY.md
index 5623a0b5..aaa68c05 100644
--- a/src/SUMMARY.md
+++ b/src/SUMMARY.md
@@ -53,6 +53,7 @@
     - [Macros](rust-2018/macros/index.md)
       - [Custom Derive](rust-2018/macros/custom-derive.md)
       - [Macro changes](rust-2018/macros/macro-changes.md)
+      - [At most one repetition](rust-2018/macros/at-most-once.md)
     - [The compiler](rust-2018/the-compiler/index.md)
       - [Improved error messages](rust-2018/the-compiler/improved-error-messages.md)
       - [Incremental Compilation for faster compiles](rust-2018/the-compiler/incremental-compilation-for-faster-compiles.md)
diff --git a/src/rust-2018/macros/at-most-once.md b/src/rust-2018/macros/at-most-once.md
new file mode 100644
index 00000000..26d13036
--- /dev/null
+++ b/src/rust-2018/macros/at-most-once.md
@@ -0,0 +1,38 @@
+# At most one repetition
+
+In Rust 2018, we have made a couple of changes to the macros-by-example syntax.
+
+1. We have added a new Kleene operator `?` which means "at most one"
+   repetition. This operator does not accept a separator token.
+2. We have disallowed using `?` as a separator to remove ambiguity with `?`.
+
+For example, consider the following Rust 2015 code:
+
+```rust
+macro_rules! foo {
+    ($a:ident, $b:expr) => {
+        println!("{}", $a);
+        println!("{}", $b);
+    }
+    ($a:ident) => {
+        println!("{}", $a);
+    }
+}
+```
+
+Macro `foo` can be called with 1 or 2 arguments; the second one is optional,
+but you need a whole other matcher to represent this possibility. This is
+annoying if your matchers are long. In Rust 2018, one can simply write the
+following:
+
+```rust
+macro_rules! foo {
+    ($a:ident $(, $b:expr)?) => {
+        println!("{}", $a);
+
+        $(
+            println!("{}", $b);
+         )?
+    }
+}
+```

From ab2c46c85c8ae11cd38fbc9e6feba4108265b75a Mon Sep 17 00:00:00 2001
From: Mark Mansi <markm@cs.wisc.edu>
Date: Mon, 3 Dec 2018 13:01:28 -0600
Subject: [PATCH 2/2] rust 2018

---
 src/rust-2018/macros/at-most-once.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/rust-2018/macros/at-most-once.md b/src/rust-2018/macros/at-most-once.md
index 26d13036..fb38610d 100644
--- a/src/rust-2018/macros/at-most-once.md
+++ b/src/rust-2018/macros/at-most-once.md
@@ -8,7 +8,7 @@ In Rust 2018, we have made a couple of changes to the macros-by-example syntax.
 
 For example, consider the following Rust 2015 code:
 
-```rust
+```rust2018
 macro_rules! foo {
     ($a:ident, $b:expr) => {
         println!("{}", $a);
@@ -25,7 +25,7 @@ but you need a whole other matcher to represent this possibility. This is
 annoying if your matchers are long. In Rust 2018, one can simply write the
 following:
 
-```rust
+```rust2018
 macro_rules! foo {
     ($a:ident $(, $b:expr)?) => {
         println!("{}", $a);