Erroneous code example:
```ignore (depends on release channel)
-#![feature(non_ascii_idents)] // error: `#![feature]` may not be used on the
- // stable release channel
+#![feature(lang_items)] // error: `#![feature]` may not be used on the
+ // stable release channel
```
If you need the feature, make sure to use a nightly release of the compiler