Add documentation for `doc(attribute = "...")` attribute

1 files changed, 18 insertions, 1 deletions

diff --git a/src/doc/rustdoc/src/unstable-features.md b/src/doc/rustdoc/src/unstable-features.md
index bb28e3abbf3..25c929a1dba 100644
--- a/src/doc/rustdoc/src/unstable-features.md
+++ b/src/doc/rustdoc/src/unstable-features.md
@@ -196,7 +196,7 @@ to enable.
 
 ### Document keywords
 
-This is for Rust compiler internal use only.
+This is for internal use in the std library.
 
 Rust keywords are documented in the standard library (look for `match` for example).
 
@@ -211,6 +211,23 @@ To do so, the `#[doc(keyword = "...")]` attribute is used. Example:
 mod empty_mod {}
 ```
 
+### Document builtin attributes
+
+This is for internal use in the std library.
+
+Rust builtin attributes are documented in the standard library (look for `repr` for example).
+
+To do so, the `#[doc(attribute = "...")]` attribute is used. Example:
+
+```rust
+#![feature(rustdoc_internals)]
+#![allow(internal_features)]
+
+/// Some documentation about the attribute.
+#[doc(attribute = "repr")]
+mod empty_mod {}
+```
+
 ### Use the Rust logo as the crate logo
 
 This is for official Rust project use only.