Consider such a paragraph in [temp.variadic], that is:

The instantiation of a pack expansion that is neither a sizeof... expression nor a fold-expression produces a list of elements E₁,E₂,...,E_N, where N is the number of elements in the pack expansion parameters. Each E_i is generated by instantiating the pattern and replacing each pack expansion parameter with its i^th element. Such an element, in the context of the instantiation, is interpreted as follows:

Please note the bolded phrase, it sounds like that the element is ascribed to Ei. However, IIUC, according to the sentence "where N is the number of elements in the pack expansion parameters", this element should refer to that of pack expansion parameters, so this sentence would make a bit misleading. For example, T...t, where T is a template parameter pack, since its pattern is T t, hence the i^th element(namely Ei) of such a list that was produced by the instantiation of this pack expansion should be Ti t where Ti would be the the i^th element of the pack expansion parameters, which denotes the corresponding template parameter .

So, would this paragraph be modified to:

The instantiation of a pack expansion that is neither a sizeof... expression nor a fold-expression produces a comma-separated list of elements, that is E₁,E₂,...,E_N, where N is the number of elements in the pack expansion parameters. Each E_i is generated by instantiating the pattern and replacing each pack expansion parameter with the i^th element of the pack expansion parameters. Such an element, in the context of the instantiation, is interpreted as follows:

Will it be more clear?