Does this actually need a version block? If yes, I think something like this would make more sense anyways:

```D
    /**
     * Detect whether type $(D T) is a Vector type.
     */
    template isVectorType(T)
    {
        enum isVectorType = false; 
    }

    version (X86_64)
    {
        template isVectorType(T : __vector(T[N]), size_t N)
        {
            enum isVectorType = true; 
        }
    }
}
```

Also, from a DDOc perspective, only the first `isVectorType` needs to be DDoc'ed.