Question

The MSDN documentation doesn’t explain in detail what its used for.

Since its optional, I almost assume its like metadata of some sort.

How I look at it right now, I’d like to use it as a way to specify caches for specific users only such as:

new CacheItem(key: "keyName", value: objectData, regionName: "userName")

What is the responsibility of the regionName property of the CacheItem class? What is it used for?

Answer 1

From Caching Application Data by Using Multiple Cache Objects in an ASP.NET Application ^(archive)

The custom class demonstrates how you would store the cached data in a
named region in memory. The built-in memory cache object does not
support the concept of regions but it is used in this blog to
demonstrate how you would implement regions in a custom cache class.
A cache region is a partition in memory that is reserved for storing
one or more cache objects. A cache region helps organize cache objects
in memory.

(my emphasis)