Update virtual table policy diagram.md

Author: thecppzoo

design/virtual table policy diagram.md

@@ -2,6 +2,18 @@
 
 ## Note: Some of the identifiers in the framework come from very old times, when the concepts where more primitive.
 
+## Terms
+
+`template<typename Policy> AnyContainer<Policy>`: The type erasure wrapper/manager
+Policy: A type that has members that configure `AnyContainer`.
+For the sub-framework of virtual-table type switching, `zoo::Policy`, the user can specify the parameters of the local buffer and all the capabilities of the wrapper/manager:
+`Policy<StorageModel, A1, A2, A2>` indicates that the local buffer has the size and alignment of `StorageModel`, typically some `void *[N]`.  The `A`s are *affordances*, the capabilities of the 
+`AnyContainer` wrapper/manager.
+The **implementation** uses the following members of a policy:
+1. `MemoryLayout`: this is the **base value manager**.  It's size and alignment are that of the `zoo::Policy` storage model.
+2. `template<typename ValueToManage> Builder`: indicates the concrete value manager for the given type
+3. `template<typename ConcreteAnyContainer> Affordances`: this provide bases from the affordances to the `AnyContainer`, this is how they add things to the interface of `AnyContainer`, via their template members `UserAffordance`, that use the CRTP [^user affordance CRTP]
+
 ## The base value manager
 
 The *policy* tells `AnyContainer` what its local storage is going to be, via the member `MemoryLayout`.  You may think of the "Memory Layout" as the base ***value manager***.
@@ -26,3 +38,10 @@ The most important feature of this flavor of the framework is to use virtual tab
     ```
    [from here](https://github.com/thecppzoo/zoo/blob/d6435fc984ee0bde31979f7908a73473f61ac4bd/inc/zoo/Any/VTablePolicy.h#L274-L276).
 
+[^user affordance CRTP]: The curiously recurring template pattern accomplishes the following:
+    For `AnyContainer<Policy<StorageModel, A1, A2, A2>>`:
+    ```c++
+        using M = AnyContainer<Policy<StorageModel, A1, A2, A2>>;
+    ```
+    then `A1::UserAffordance<M>` is a base class of `M`; if there is a function member `std::string stringize() const` in `A1::UserAffordance<M>`, then for an object `m` of `M`, you can invoke `m.stringize()`.
+