consider to use the demo from coderefineary for visibility levels

content/targets-new-visibility-levels.rst

@@ -0,0 +1,44 @@
+.. _targets-new-visibility-levels:
+
+Visibility levels (Code from Coderefineary)
+-------------------------------------------
+
+
+Visibility levels ``PRIVATE``, ``PUBLIC``, or ``INTERFACE`` are very powerful and herein we will briefly demonstrate their difference.
+
+
+In this demo, we split the source code into 3 libraries and all files are available in the ``content/code/xx_visibility-levels/`` folder.
+
+	.
+	├── CMakeLists.txt
+	├── greeting
+	│   ├── greeting.cpp
+	│   └── greeting.hpp
+	├── hello_world
+	│   ├── hello_world.cpp
+	│   └── hello_world.hpp
+	├── main.cpp
+	└── world
+		├── world.cpp
+		└── world.hpp
+
+
+In this source code, the main function links to greeting which links to hello_world which links to world.
+
+
+.. typealong:: The internal dependency tree
+
+   If you have installed ``Graphviz``, you can visualize the dependencies between these targets:
+
+   .. code-block:: console
+
+      $ cd build
+      $ cmake --graphviz=project.dot ..
+      $ dot -T svg project.dot -o project.svg
+
+   .. figure:: img/project.svg
+      :align: center
+
+      The dependencies between the four targets in the code example.
+
+