+ * \param index is the slot index.
+ *
+ * \param level is the indexing level to access. Level 0 is the leaf
+ * level that holds the slots for the items; level 1 is one level up,
+ * for vectors larger than 256 items; ans so on.
+ *
+ * \param add is a flag to indicate (with 1) that missing index pages
+ * should be added, or (with 0) that the function should simply return
+ * null if an index page to access at any level is missing.
+ *
+ * \returns a pointer to the slot for the indexed item (level 0), or
+ * (for higher levels) the slot for the index page on the access path
+ * to the indexed item. The function returns 0 if the access path is
+ * broken by a missing index page, or (with add==1) the allocation of
+ * a new index page fails.
+ *
+ * \note The index tree for the vector is populated on demand only
+ * where access has been requested.
+ *
+ * \related vector
+ */
+extern void **vector_access(vector *pv,vector_index index,int level,int add);
+
+/**
+ * \brief Return the slot value at the given index.
+ *
+ * \param pv is the vector concerned.
+ *
+ * \param index is the slot index.