Improved documentation for GDScript `in` keyword (#5883)

* Improve 'in' operator description

* Apply syntax suggestions from code review

Co-authored-by: Hugo Locurcio <[email protected]>

tutorials/scripting/gdscript/gdscript_basics.rst

@@ -264,7 +264,12 @@ The following is the list of supported operators and their precedence.
 +--------------------------------------------------------------------------------+-------------------------------------------+
 | ``<`` ``>`` ``==`` ``!=`` ``>=`` ``<=``                                        | Comparisons                               |
 +--------------------------------------------------------------------------------+-------------------------------------------+
-| ``in``                                                                         | Content test                              |
+| ``in``                                                                         | When used with the ``if`` keyword it      |
+|                                                                                | checks if a value is within a string,     |
+|                                                                                | list, range, dictionary, or node.         |
+|                                                                                | When used with the ``for`` keyword it is  |
+|                                                                                | used to iterate though the contents of a  |
+|                                                                                | string, list, range, dictionary or node.  |
 +--------------------------------------------------------------------------------+-------------------------------------------+
 | ``not``                                                                        | Boolean NOT                               |
 +--------------------------------------------------------------------------------+-------------------------------------------+
@@ -1046,6 +1051,16 @@ multiple lines to preserve readability::
             else "orange"
     print(fruit_alt)  # banana
 
+You may also wish to check if a value is contained within something. You can
+use an ``if`` statement combined with the ``in`` operator to accomplish this::
+
+    # Check if a letter is in a string.
+    var text = "abc"
+    if 'b' in text: print("The string contains b")
+
+    # Check if a variable is contained within a node.
+    if "varName" in get_parent(): print("varName is defined in parent!")
+
 while
 ^^^^^