Add more expression function examples to style guide.

style.md

@@ -298,7 +298,34 @@ override fun toString(): String {
 override fun toString(): String = "Hey"
 ```
 
-Expression functions should not wrap to two lines. If an expression function grows to require wrapping, use a normal function body, a `return` declaration, and normal expression wrapping rules instead.
+If an expression function's return grows to require wrapping, use a normal function body, a `return` declaration, and normal expression wrapping rules instead.
+
+```kotlin
+// Okay
+fun veryVeryLongFun() =
+        callsAVeryVeryLongFunctionWithHorribleName(andTonsAndTonsOfParameters)
+
+// WRONG!
+fun veryVeryLongFun() =
+        callsAVeryVeryLongFunctionWithHorribleName(andTonsAndTonsOfParameters,
+                andMoreParameters)
+
+// Okay
+fun veryVeryLongFun() {
+        return callsAVeryVeryLongFunctionWithHorribleName(andTonsAndTonsOfParameters,
+                andMoreParameters)
+}
+```
+
+Multiline expression functions are allowed providing it returns a single expression.
+
+```kotlin
+fun getFoo(index: Int) = when (index) {
+    in 0..10 -> "foo"
+    in 11..20 -> "bar"
+    else -> "baz"
+}
+```
 
 ### Properties