| 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). | |
| Erroneous code example: | |
| ```compile_fail,E0522 | |
| #![feature(lang_items)] | |
| #[lang = "cookie"] | |
| fn cookie() -> ! { // error: definition of an unknown language item: `cookie` | |
| loop {} | |
| } | |
| ``` |