what is mean "v.template is

c++ code

template <typename F, typename V, typename R, typename T, typename... Types>
struct dispatcher<F, V, R, T, Types...>
{
    VARIANT_INLINE static R apply_const(V const& v, F&& f)
    {
        if (v.template is<T>())
        {
            return f(unwrapper<T>::apply_const(v.template get_unchecked<T>()));
        }
        else
        {
            return dispatcher<F, V, R, Types...>::apply_const(v, std::forward<F>(f));
        }
    }

    VARIANT_INLINE static R apply(V& v, F&& f)
    {
        if (v.template is<T>())
        {
            return f(unwrapper<T>::apply(v.template get_unchecked<T>()));
        }
        else
        {
            return dispatcher<F, V, R, Types...>::apply(v, std::forward<F>(f));
        }
    }
};

what is mean v.template is<T>() in this c++ prog? i cannot find any "is" function, this v.template is<T>() is system inner function or keyword with v.template get_unchecked<T>().