What is the difference between D3D12 structures/functions with terminal 1 in the name and without?

I could not figure out the difference between for instance CD3DX12_DESCRIPTOR_RANGE and CD3DX12_DESCRIPTOR_RANGE1.

Why do both exist? Which should I use? Is there a general rule of behavior/usage/recommendation for all structures and functions with both naming?

Looking at the documentation the D3D12_DESCRIPTOR_RANGE1 structure has one extra member D3D12_DESCRIPTOR_RANGE_FLAGS Flags; to
• Root Signature 1.1 was introduced with Windows 10 Anniversary Update (14393) so that API doesn't work on Windows 10 (10240) or Windows 10 November 2015 (10586). That's also why the D3DX12 helper D3DX12SerializeVersionedRootSignature was introduced to handle it. – Chuck Walbourn Mar 21 at 6:30