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+An undeclared lifetime was used.
+
+Erroneous code example:
+
+```compile_fail,E0261
+// error, use of undeclared lifetime name `'a`
+fn foo(x: &'a str) { }
+
+struct Foo {
+    // error, use of undeclared lifetime name `'a`
+    x: &'a str,
+}
+```
+
+These can be fixed by declaring lifetime parameters:
+
+```
+struct Foo<'a> {
+    x: &'a str,
+}
+
+fn foo<'a>(x: &'a str) {}
+```
+
+Impl blocks declare lifetime parameters separately. You need to add lifetime
+parameters to an impl block if you're implementing a type that has a lifetime
+parameter of its own.
+For example:
+
+```compile_fail,E0261
+struct Foo<'a> {
+    x: &'a str,
+}
+
+// error,  use of undeclared lifetime name `'a`
+impl Foo<'a> {
+    fn foo<'a>(x: &'a str) {}
+}
+```
+
+This is fixed by declaring the impl block like this:
+
+```
+struct Foo<'a> {
+    x: &'a str,
+}
+
+// correct
+impl<'a> Foo<'a> {
+    fn foo(x: &'a str) {}
+}
+```