Added suggested notes

* Note on while loop not supporting named breaks.
* Note on hygienic macros (and example of such within loops)

Author: noam

src/doc/guide-lifetimes.md

@@ -559,13 +559,13 @@ points at a static constant).
 
 # Named lifetimes
 
-Lifetimes can be named and referenced. For example, the special lifetime 
+Lifetimes can be named and referenced. For example, the special lifetime
 `'static`, which does not go out of scope, can be used to create global
 variables and communicate between tasks (see the manual for usecases).
 
 ## Parameter Lifetimes
 
-Named lifetimes allow for grouping of parameters by lifetime. 
+Named lifetimes allow for grouping of parameters by lifetime.
 For example, consider this function:
 
 ~~~
@@ -674,6 +674,11 @@ Named lifetime notation can also be used to control the flow of execution:
 }
 ~~~
 
+> ***Note:*** Labelled breaks are not currently supported within `while` loops.
+
+Named labels are hygienic and can be used safely within macros.
+See the macros guide section on hygiene for more details.
+
 # Conclusion
 
 So there you have it: a (relatively) brief tour of the lifetime

src/doc/guide-macros.md

@@ -398,6 +398,38 @@ position (in particular, not as an argument to yet another macro invocation),
 the expander will then proceed to evaluate `m2!()` (along with any other macro
 invocations `m1!(m2!())` produced).
 
+# Hygiene
+
+To prevent clashes, rust implements
+[hygienic macros](http://en.wikipedia.org/wiki/Hygienic_macro).
+
+As an example, `loop` and `for-loop` labels (discussed in the lifetimes guide)
+will not clash. The following code will print "Hello!" only once:
+
+~~~
+#[feature(macro_rules)];
+
+macro_rules! loop_x (
+    ($e: expr) => (
+        // $e will not interact with this 'x
+        'x: loop {
+            println!("Hello!");
+            $e
+        }
+    );
+)
+
+fn main() {
+    'x: loop {
+        loop_x!(break 'x);
+        println!("I am never printed.");
+    }
+}
+~~~
+
+The two `'x` names did not clash, which would have caused the loop
+to print "I am never printed" and to run forever.
+
 # A final note
 
 Macros, as currently implemented, are not for the faint of heart. Even