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+The lang attribute was used in an invalid context.
+
+Erroneous code example:
+
+```compile_fail,E0522
+#![feature(lang_items)]
+
+#[lang = "cookie"]
+fn cookie() -> ! { // error: definition of an unknown language item: `cookie`
+    loop {}
+}
+```
+
+The lang attribute is intended for marking special items that are built-in to
+Rust itself. This includes special traits (like `Copy` and `Sized`) that affect
+how the compiler behaves, as well as special functions that may be automatically
+invoked (such as the handler for out-of-bounds accesses when indexing a slice).