Added fall-through documentation & return notation (#19428)

* Added fall-through documentation & return notation

Fall-through is an important feature of switch statements. In addition, best practices with break-usage have been included.

* fix: added closing switch curly braces

* fix: corrected link syntax

client/src/pages/guide/english/php/switch/index.md

@@ -19,7 +19,8 @@ In PHP, the `Switch` statement is very similar to the Javascript `Switch` statem
     	    echo "i is camp";
     	    break;
     	default:
-    		echo "i is freecodecamp";
+    	    echo "i is freecodecamp";
+            break;
 	}
 
 ```
@@ -27,5 +28,61 @@ In PHP, the `Switch` statement is very similar to the Javascript `Switch` statem
 ### Break
 The `break;` statement exits the switch and goes on to run the rest of the application's code. If you do not use the `break;` statement you may end up running mulitple cases and statements, sometimes this may be desired in which case you should not include the `break;` statement.
 
+An example of this behavior can be seen below:
+
+```
+<?php
+    $j = 0
+
+    switch ($i) {
+        case '2':
+            $j++;
+        case '1':
+            $j++;
+            break;
+        default:
+            break;
+    }
+```
+
+If $i = 1, the value of $j would be:
+
+```
+1
+```
+
+If $i = 2, the value of $j would be:
+
+```
+2
+```
+
+While break can be omitted without causing fall-through in some instances (see below), it is generally best practice to include it for legibility and safety (see below):
+
+```
+<?php
+    switch ($i) {
+        case '1':
+            return 1;
+        case '2':
+            return 2;
+        default:
+            break;
+     }
+```
+```
+<?php
+    switch ($i) {
+        case '1':
+            return 1;
+            break;
+        case '2':
+            return 2;
+            break;
+        default:
+            break;
+     }
+```
+
 #### More Information:
-* <a href="https://secure.php.net/manual/en/control-structures.switch.php" rel="nofollow">php.net docs Switch</a>
+* [php.net docs Switch](https://secure.php.net/manual/en/control-structures.switch.php")