Overwork documentation (#4516)

docs/mkdocs/docs/api/ordered_json.md

@@ -6,6 +6,13 @@ using ordered_json = basic_json<ordered_map>;
 
 This type preserves the insertion order of object keys.
 
+## Iterator invalidation
+
+The type is based on [`ordered_map`](ordered_map.md) which in turn uses a `std::vector` to store object elements.
+Therefore, adding object elements can yield a reallocation in which case all iterators (including the
+[`end()`](basic_json/end.md) iterator) and all references to the elements are invalidated. Also, any iterator or
+reference after the insertion point will point to the same index which is now a different value.
+
 ## Examples
 
 ??? example