What is the difference between pages under dlang.org/phobos and dlang.org/library?

[A D dev via Digitalmars-d-learn]

Hi list,

What is the difference between pages under dlang.org/phobos and 
dlang.org/library?
And when should we use which, as a reference?
E.g.

https://dlang.org/phobos/std_zip.html

https://dlang.org/library/std/zip.html

I viewed the above two pages and the content seems roughly the 
same. How to know which one is more up to date and should be 
used? Same question for all other such similar pages on the two 
sites. Is there any thumb rule for this?

Thanks.