Why is the sequence of the $ _ SERVER array different in different browsers?

Why is the $ _ SERVER array order different from that of print_r ($ _ SERVER) in different browsers? array sorting is different in chrome and ie. why?

Reply to discussion (solution)

$ _ SERVER Keys starting with HTTP _ are transmitted by the requester.
Different sorting order should be related to the order in the request http header

But what is the relationship?

You should look at the F function Source code .....
No return value. Therefore, it is null by default.

I don't think it's okay. What's less important is whether the array content is consistent.

,..... An error message is posted !!!!!