Template parameter pack that does not participate in template argument deduction

According to [temp.deduct.call]

Template argument deduction is done by comparing each function template parameter type (call it P) that contains template-parameters that participate in template argument deduction with the type of the corresponding argument of the call (call it A) as described below.

In most cases, the types, templates, and non-type values that are used to compose P participate in template argument deduction.

In this example

template<class...T, class U>
void fun(U);
int main(){
   fun(0);  //#1
}

As per the above rule, the template parameter pack does not participate in template argument deduction. If there were no other special rule specified, as per

if any template argument remains neither deduced nor explicitly specified, template argument deduction fails.

The deduction would fail since the template argument for the template parameter pack is neither deduced(the pack does not participate in the deduction process) nor explicitly specified.

However, in the older standard, there's a special rule states that:

A trailing template parameter pack ([temp.variadic]) not otherwise deduced will be deduced as an empty sequence of template arguments.

However, such a normative rule has become a note in the current draft. I think such a rule should be a normative rule since there's no other alternative rule that states similar things. Making it to be a note is not persuasive to explain why can #1 be otherwise deduced successfully.

Read the [temp.deduct.call] wording, the note linked from [temp.arg.explicit], and the example involving template<class...T, class U> void fun(U). Determine how the trailing, otherwise-undeduced pack is specified and update the draft so the successful deduction in #1 has a clear normative basis.