Tie::dxhash implements a hash which preserves insertion order and allows duplicate keys.

tie::dxhash works by storing the hash data in an array of hash references (containing the key/value pairs). this preserves insertion order. a separate set of iterators (one per distinct key) keeps track of the last retrieved value for a given key, thus allowing the successive retrieval of multiple values for the same key to work as expected.

tie::dxhash was originally written to facilitate the use of more complex mod_rewrite rules in apache configuration files written with perl sections.