it also states in section 6.7.7 (“type names”) that

If the pointer operand points to an element of an array object, and the array is large enough, the result points to an element offset from the original element such that the difference of the subscripts of the resulting and original array elements equals the integer expression.

note also that your example is the only occurrence of the word “index” in the entire document that isn’t just referring to the actual index at the end.