+// Really? ^^ The INCLUDE_LAYER(class) macro is defined in a cpp file and
+// is undefined a few lines later. In fact the INCLUDE_LAYER is only
+// used in the layer.cpp file and the functionality is the same. Even
+// more, I think that we should use register_in_book call because maybe
+// the Layer class would like to do something else when register the class.
+//! Register a Layer class in the book of layers