Let me start with the second question:

Or, when I do Items => {... }, this list already "digested" in a hash form thus not feasible to access like an array anymore?

That's correct. As soon as Perl has processed it into a hash reference, the original order of key/value pairs is lost. This gives the answer to the first question:

I know that's not an ARRAY ref, but since I want to learn the appear order, can I do anything to access this HASH ref like other ordinary array ( they still a list right) ?

A hash is neither an array nor a list. You can convert a hash to an array like my @array = %hash, but then you get random ordering of the key/value pairs.

So, if you want to retain information about the ordering, then you can:

• either process the key/value pairs while they are still in the caller's order in @_, before converting them to a hash,
• or use some CPAN module like Hash::Ordered which creates "hashes with ordered keys".