src: add comments about implicit dependencies

src/base-object.h

@@ -40,6 +40,11 @@ class BaseObject {
 
   inline Environment* env() const;
 
+  // The handle_ must have an internal field count > 0, and the first
+  // index is reserved for a pointer to this class. This is an
+  // implicit requirement, but Node does not have a case where it's
+  // required that MakeWeak() be called and the internal field not
+  // be set.
   template <typename Type>
   inline void MakeWeak(Type* ptr);
 

src/node_crypto.h

@@ -120,6 +120,8 @@ class SecureContext : public BaseObject {
   }
 };
 
+// SSLWrap implicitly depends on the inheriting class' handle having an
+// internal pointer to the Base class.
 template <class Base>
 class SSLWrap {
  public:
@@ -217,6 +219,9 @@ class SSLWrap {
   friend class SecureContext;
 };
 
+// Connection inherits from AsyncWrap because SSLWrap makes calls to
+// MakeCallback, but SSLWrap doesn't store the handle itself. Instead it
+// assumes that any args.This() called will be the handle from Connection.
 class Connection : public SSLWrap<Connection>, public AsyncWrap {
  public:
   ~Connection() {