+/**
+ * \brief stack for BER constructed items
+ *
+ * data structure for con stack.. a little peculiar. Since we can't
+ * deallocate memory we reuse stack items (popped items gets reused)
+ *
+ *\verbatim
+ * +---+ +---+ +---+ +---+
+ * NULL -|p n|-----|p n|-----|p n|-----|p n|-- NULL
+ * +---+ +---+ +---+ +---+
+ * | |
+ * stack_first stack_top reused item
+ *\endverbatim
+ */
+struct odr_constack