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+Only traits defined in the current crate can be implemented for arbitrary types.
+
+Erroneous code example:
+
+```compile_fail,E0117
+impl Drop for u32 {}
+```
+
+This error indicates a violation of one of Rust's orphan rules for trait
+implementations. The rule prohibits any implementation of a foreign trait (a
+trait defined in another crate) where
+
+ - the type that is implementing the trait is foreign
+ - all of the parameters being passed to the trait (if there are any) are also
+   foreign.
+
+To avoid this kind of error, ensure that at least one local type is referenced
+by the `impl`:
+
+```
+pub struct Foo; // you define your type in your crate
+
+impl Drop for Foo { // and you can implement the trait on it!
+    // code of trait implementation here
+#   fn drop(&mut self) { }
+}
+
+impl From<Foo> for i32 { // or you use a type from your crate as
+                         // a type parameter
+    fn from(i: Foo) -> i32 {
+        0
+    }
+}
+```
+
+Alternatively, define a trait locally and implement that instead:
+
+```
+trait Bar {
+    fn get(&self) -> usize;
+}
+
+impl Bar for u32 {
+    fn get(&self) -> usize { 0 }
+}
+```
+
+For information on the design of the orphan rules, see [RFC 1023].
+
+[RFC 1023]: https://github.com/rust-lang/rfcs/blob/master/text/1023-rebalancing-coherence.md