[FEATURE] Explain how to use the accordion directive

Documentation/WritingReST/Reference/Content/Accordion.rst

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+..  include:: /Includes.rst.txt
+..  highlight:: rst
+..  index:: reST; Accordion
+..  _rest-accordion:
+
+=========
+Accordion
+=========
+
+..  accordion::
+    :name: accordionExample
+
+    ..  accordion-item:: Accordion Item #1
+        :name: headingOne
+        :header-level: 2
+        :show:
+
+        **This is the first item's accordion body.** It is shown by default, until the collapse plugin adds the
+        appropriate classes that we use to style each element. These classes control the overall appearance,
+        as well as the showing and hiding via CSS transitions.
+
+        You can modify any of this with custom CSS
+        or overriding our default variables. It's also worth noting that just about any HTML can go within
+        the `.accordion-body`, though the transition does limit overflow.
+
+    ..  accordion-item:: Accordion Item #2
+        :name: headingTwo
+        :header-level: 2
+
+        Placeholder content for this accordion, which is intended to demonstrate the .accordion-flush class.
+        This is the second item's accordion body. Let's imagine this being filled with some actual content.
+
+    ..  accordion-item:: Accordion Item #3
+        :name: headingThree
+        :header-level: 2
+
+        Placeholder content for this accordion, which is intended to demonstrate the .accordion-flush class.
+        This is the third item's accordion body. Nothing more exciting happening here in terms of content, but
+        just filling up the space to make it look,
+        at least at first glance, a bit more representative of how this would look in a real-world application.
+
+..  code-block:: rst
+    :caption: EXT:my_extension/Documentation/SomeFile.rst
+
+    ..  accordion::
+        :name: accordionExample
+
+        ..  accordion-item:: Accordion Item #1
+            :name: headingOne
+            :header-level: 2
+            :show:
+
+            **This is the first item's accordion body.** It is shown by default, [..]
+        ..  accordion-item:: Accordion Item #2
+            :name: headingTwo
+            :header-level: 2
+
+            Placeholder content for this accordion [..]
+
+        ..  accordion-item:: Accordion Item #3
+            :name: headingThree
+            :header-level: 2
+
+            Placeholder content for this accordion [..]
+
+Accordion all closed
+====================
+
+..  accordion::
+    :name: accordionExample2
+
+    ..  accordion-item:: Accordion Item #1
+        :name: headingOne2
+        :header-level: 3
+
+        Placeholder content for this accordion
+
+    ..  accordion-item:: Accordion Item #2
+        :name: headingTwo2
+        :header-level: 3
+
+        Placeholder content for this accordion
+
+    ..  accordion-item:: Accordion Item #3
+        :name: headingThree2
+        :header-level: 3
+
+         Let's imagine this being filled with some actual content.
+
+..  code-block:: rst
+    :caption: EXT:my_extension/Documentation/SomeFile.rst
+
+    ..  accordion::
+        :name: accordionExample2
+
+        ..  accordion-item:: Accordion Item #1
+            :name: headingOne2
+            :header-level: 3
+
+            Placeholder content for this accordion
+
+        ..  accordion-item:: Accordion Item #2
+            :name: headingTwo2
+            :header-level: 3
+
+            Placeholder content for this accordion
+
+        ..  accordion-item:: Accordion Item #3
+            :name: headingThree2
+            :header-level: 3
+
+             Let's imagine this being filled with some actual content.
+
+Accordion with complex content
+==============================
+
+..  accordion::
+    :name: accordionExample3
+
+    ..  accordion-item:: Accordion Item #1
+        :name: headingOne3
+        :header-level: 3
+
+        .. tabs::
+
+           .. tab:: Apples
+
+              Apples are green, or sometimes red.
+
+           .. tab:: Pears
+
+              Pears are green.
+
+           .. tab:: Oranges
+
+              Oranges are orange.
+
+    ..  accordion-item:: Accordion Item #2
+        :name: headingTwo3
+        :header-level: 3
+        :show:
+
+        ..  code-block:: javascript
+
+            var makeNoise = function() {
+              console.log("Pling!");
+            };
+
+            makeNoise();
+            // → Pling!
+
+            var power = function(base, exponent) {
+              var result = 1;
+              for (var count = 0; count < exponent; count++)
+                result *= base;
+              return result;
+            };
+
+            console.log(power(2, 10));
+            // → 1024
+
+    ..  accordion-item:: Accordion Item #3
+        :name: headingThree3
+        :header-level: 3
+
+        .. image:: /Images/q150_ffffff.png
+           :alt: Image with background color #ffffff
+           :class: with-border with-shadow
+
+..  code-block:: rst
+    :caption: EXT:my_extension/Documentation/SomeFile.rst
+
+    ..  accordion::
+        :name: accordionExample3
+
+        ..  accordion-item:: Accordion Item #1
+            :name: headingOne3
+            :header-level: 3
+
+            .. tabs::
+
+               .. tab:: Apples
+
+                  Apples are green, or sometimes red.
+
+               .. tab:: Pears
+
+                  Pears are green.
+
+               .. tab:: Oranges
+
+                  Oranges are orange.
+
+        ..  accordion-item:: Accordion Item #2
+            :name: headingTwo3
+            :header-level: 3
+            :show:
+
+            ..  code-block:: javascript
+
+                [...]
+
+        ..  accordion-item:: Accordion Item #3
+            :name: headingThree3
+            :header-level: 3
+
+            .. image:: /Images/q150_ffffff.png
+               :alt: Image with background color #ffffff
+               :class: with-border with-shadow