ARKit, Xcode, and iOS 11 upgrade I have El Capital 10.11.6 and I do not wish to upgrade, however I need to clarify whether this means I cannot download and experiment with ARKit?

The latest Xcode version that is compatible with El Capitan is 8.2.1 but when trying to download ARKit, it suggests using Xcode 9.x so I wonder if this is just a suggestion or absolute requirement?

In other words, the fact that I would like to remain in El Capitan and Xcode 8.2.1 definitely means that I can never download and use ARKit. Correct?
In order to develop ARKit apps you need to use Xcode 9.x. Xcide 8.2.x does not include ARKit.

From Apple's Developer page:


  Get Started with ARKit
  
  Xcode 9 and iOS 11 Download iOS 11 and the latest version of Xcode 9,
  which includes the iOS 11 SDK to build AR features in your app today.