[Accepted as a DR at the February, 2019 meeting.]

Although it is not possible to specify a constructor's template arguments in a constructor invocation (because the constructor has no name but is invoked by use of the constructor's class's name), it is possible to “name” the constructor in declarative contexts: per 6.5.5.2 [class.qual] paragraph 2,

In a lookup in which the constructor is an acceptable lookup result, if the nested-name-specifier nominates a class C, and the name specified after the nested-name-specifier, when looked up in C, is the injected-class-name of C ( Clause 11 [class]), the name is instead considered to name the constructor of class C... Such a constructor name shall be used only in the declarator-id of a declaration that names a constructor.

Should it therefore be possible to specify template-arguments for a templated constructor in an explicit instantiation or specialization? For example,

    template <int dim> struct T {};
    struct X {
      template <int dim> X (T<dim> &) {};
    };

    template X::X<> (T<2> &);

If so, that should be clarified in the text. In particular, 11.4.5 [class.ctor] paragraph 1 says,

Constructors do not have names. A special declarator syntax using an optional sequence of function-specifiers (9.2.3 [dcl.fct.spec]) followed by the constructor's class name followed by a parameter list is used to declare or define the constructor.

This certainly sounds as if the parameter list must immediately follow the class name, with no allowance for a template argument list.

It would be worthwhile in any event to revise this wording to utilize the “considered to name” approach of 6.5.5.2 [class.qual]; as it stands, this wording sounds as if the following would be acceptable:

    struct S {
        S();
    };
    S() { }    // qualified-id not required?