Although it would probably be fitting to describe it as a subset. If you look at vision, then it is a spectrum that includes everyone. Even blind people. If you are looking at blindness, then it is a subset of the vision spectrum that only includes people that meet certain other criteria, i.e. below a certain threshold of vision. Same for autism disorder. Every human is on a mentality spectrum, and autism is a subset of that.
No. Blindness is also a spectrum but not everyone is blind. There is a range of normal vision and someone is only blind if they fall outside of that range. However, two people who are deemed blind can have varying degrees of blindness and need varying degrees of assistance.
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