diff --git a/single_file_tests/format.rs b/single_file_tests/format.rs
index b21c3e9..a3b76c9 100644
--- a/single_file_tests/format.rs
+++ b/single_file_tests/format.rs
@@ -1,4 +1,6 @@
 
+// format:
+// { [argument] ':' [[fill] align] [sign] ['#'] [width [$]] ['.' precision [$]] [type] }
 fn main() {
     let a = 1111111;
 
@@ -8,4 +10,8 @@ fn main() {
     println!("octet: {:o}", a);
     println!("0x{:x}", a);
     println!("0x{:X}", a);
+
+    println!("{0} {1}", "AA", "BB");
+    println!("{a} {b}", a = "AA", b = "BB");
+    println!("[{a:^6}] [{b:<6}] [{b:>6}] [{c:<10.3}]", a = "AA", b = "BB", c = 111.1);
 }
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