Emphasize 'mock' variable name exception in docs (#8182)

docs/Es6ClassMocks.md

@@ -145,7 +145,18 @@ jest.mock('./sound-player', () => {
 });
 ```
 
-A limitation with the factory parameter is that, since calls to `jest.mock()` are hoisted to the top of the file, it's not possible to first define a variable and then use it in the factory. An exception is made for variables that start with the word 'mock'. It's up to you to guarantee that they will be initialized on time!
+A limitation with the factory parameter is that, since calls to `jest.mock()` are hoisted to the top of the file, it's not possible to first define a variable and then use it in the factory. An exception is made for variables that start with the word 'mock'. It's up to you to guarantee that they will be initialized on time! For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration:
+
+```javascript
+// Note: this will fail
+import SoundPlayer from './sound-player';
+const fakePlaySoundFile = jest.fn();
+jest.mock('./sound-player', () => {
+  return jest.fn().mockImplementation(() => {
+    return {playSoundFile: fakePlaySoundFile};
+  });
+});
+```
 
 ### Replacing the mock using [`mockImplementation()`](MockFunctionAPI.md#mockfnmockimplementationfn) or [`mockImplementationOnce()`](MockFunctionAPI.md#mockfnmockimplementationoncefn)
 

website/versioned_docs/version-23.x/Es6ClassMocks.md

@@ -146,7 +146,18 @@ jest.mock('./sound-player', () => {
 });
 ```
 
-A limitation with the factory parameter is that, since calls to `jest.mock()` are hoisted to the top of the file, it's not possible to first define a variable and then use it in the factory. An exception is made for variables that start with the word 'mock'. It's up to you to guarantee that they will be initialized on time!
+A limitation with the factory parameter is that, since calls to `jest.mock()` are hoisted to the top of the file, it's not possible to first define a variable and then use it in the factory. An exception is made for variables that start with the word 'mock'. It's up to you to guarantee that they will be initialized on time! For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration:
+
+```javascript
+// Note: this will fail
+import SoundPlayer from './sound-player';
+const fakePlaySoundFile = jest.fn();
+jest.mock('./sound-player', () => {
+  return jest.fn().mockImplementation(() => {
+    return {playSoundFile: fakePlaySoundFile};
+  });
+});
+```
 
 ### Replacing the mock using [`mockImplementation()`](MockFunctionAPI.md#mockfnmockimplementationfn) or [`mockImplementationOnce()`](MockFunctionAPI.md#mockfnmockimplementationoncefn)
 

website/versioned_docs/version-24.0/Es6ClassMocks.md

@@ -146,7 +146,18 @@ jest.mock('./sound-player', () => {
 });
 ```
 
-A limitation with the factory parameter is that, since calls to `jest.mock()` are hoisted to the top of the file, it's not possible to first define a variable and then use it in the factory. An exception is made for variables that start with the word 'mock'. It's up to you to guarantee that they will be initialized on time!
+A limitation with the factory parameter is that, since calls to `jest.mock()` are hoisted to the top of the file, it's not possible to first define a variable and then use it in the factory. An exception is made for variables that start with the word 'mock'. It's up to you to guarantee that they will be initialized on time! For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration:
+
+```javascript
+// Note: this will fail
+import SoundPlayer from './sound-player';
+const fakePlaySoundFile = jest.fn();
+jest.mock('./sound-player', () => {
+  return jest.fn().mockImplementation(() => {
+    return {playSoundFile: fakePlaySoundFile};
+  });
+});
+```
 
 ### Replacing the mock using [`mockImplementation()`](MockFunctionAPI.md#mockfnmockimplementationfn) or [`mockImplementationOnce()`](MockFunctionAPI.md#mockfnmockimplementationoncefn)