diff --git a/doc/src/ch02-lang/ch04-macros/ch01-builtins.md b/doc/src/ch02-lang/ch04-macros/ch01-builtins.md
index b040aab..2494c3e 100644
--- a/doc/src/ch02-lang/ch04-macros/ch01-builtins.md
+++ b/doc/src/ch02-lang/ch04-macros/ch01-builtins.md
@@ -149,4 +149,28 @@ The fully expanded source would look like:
 push32 0xa9059cbb2ab09eb219583f4a59a5d0623ade346d962bcd4e46b11da047c9049b
 ```
 
+## Hardfork selection
+
+### `%hardfork(...)`
+
+The `%hardfork` macro is useful when you want to restrict the hardfork range in which the code can be compiled.
+
+For example:
+
+```rust
+# extern crate etk_asm;
+# extern crate etk_ops;
+# let src = r#"
+%hardfork(">london,<=cancun")
+
+push 0x08
+# "#;
+# let mut output = Vec::new();
+# let mut ingest = etk_asm::ingest::Ingest::new(&mut output, etk_ops::HardFork::Cancun);
+# ingest.ingest(file!(), src).unwrap();
+# assert_eq!(output, &[0x60, 0x02, 0x5b]);
+```
+
+can only be compiled by specifying a hardfork using the `--hardfork` flag (the latest hardfork available by default) strictly after `London` and equal or older than `Cancun`.
+
 [abi]: https://docs.soliditylang.org/en/latest/abi-spec.html#function-selector