[Doc] Improve documentation PropertyContainer

src/Base/Persistence.h

@@ -39,11 +39,14 @@ class BaseExport Persistence: public BaseClass
     TYPESYSTEM_HEADER();
 
 public:
-    /** This method is used to get the size of objects
-     * It is not meant to have the exact size, it is more or less an estimation
-     * which runs fast! Is it two bytes or a GB?
+    /**
+     * @brief Get the size of objects.
+     *
+     * It is not meant to have the exact size, it is more or less a fast
+     * estimation to tell whether it is two bytes or a GB.
      */
     virtual unsigned int getMemSize() const = 0;
+
     /** This method is used to save properties to an XML document.
      * A good example you'll find in PropertyStandard.cpp, e.g. the vector:
      * \code