SG_BEGIN_DECL()
+/** Container for all the objects of a given type
+ *
+ * * each item is identified by a string name/identifier;
+ *
+ * * the lib itself is a dictionary from the element id to the element;
+ *
+ * * the element itself is represented aby the xbt_dictelm_t;
+ *
+ * * the element can store any number of associated facets/data structures
+ * (corresponding to the different layers of SimGrid or its extensions)
+ * in ((void**)dictelt->content)[level];
+ *
+ * * each level is allocated in the lib with `xbt_lib_add_level`.
+ *
+ * <pre>
+ * // Define a collection for the foo objects and two associated facets:
+ * typedef xbt_dictelm_t foo_t;
+ * xbt_lib_t foo_lib = xbt_lib_new();
+ * int BAR_FOO_LEVEL = xbt_lib_add_level(foo_lib, free_bar);
+ * int AUTH_FOO_LEVEL = xbt_lib_add_level(foo_lib, free_auth);
+ *
+ * // Store a bar:
+ * bar_t bar = bar_new();
+ * char* id = bar_name(bar);
+ * xbt_lib_set(id, id, BAR_FOO_LEVEL, bar);
+ *
+ * // Find the corresponding foo and the facet again:
+ * foo_t foo = xbt_lib_get_elm_or_null(foo_lib, id);
+ * bar_t bar2 = (bar_t) xbt_lib_get_level(foo, BAR_FOO_LEVEL);
+ * assert(bar == bar2);
+ *
+ * // Add authentication facet for the previous object:
+ * auth_t auth = auth_new();
+ * xbt_lib_set(foo_lib, id, AUTH_FOO_LEVEL, auth);
+ * </pre>
+ */
typedef struct s_xbt_lib {
xbt_dict_t dict;
int levels;
