CWG2273 Inheriting constructors vs implicit default constructor

Also fixes CWG2277.

Author: Dawn Perchik

source/declarations.tex

@@ -3022,7 +3022,8 @@
 
 \pnum
 \indextext{overloading!using-declaration and}%
-For the purpose of overload resolution, the functions that are
+For the purpose of forming a set of candidates during overload resolution,
+the functions that are
 introduced by a \grammarterm{using-declaration} into a derived class
 are treated as though they were members of the derived class. In
 particular, the implicit \tcode{this} parameter shall be treated as if
@@ -3037,6 +3038,10 @@
 of an object of class type, all subobjects other than the base class
 from which the constructor originated
 are implicitly initialized~(\ref{class.inhctor.init}).
+\begin{note}
+A member of a derived class is sometimes preferred to a member of a base class
+if they would otherwise be ambiguous~(\ref{over.match.best}).
+\end{note}
 
 \pnum
 \indextext{access control!using-declaration and}%

source/overloading.tex

@@ -1676,6 +1676,29 @@
 according to the partial ordering rules described in~\ref{temp.func.order},
 or, if not that,
 
+\item
+\tcode{F1} is a constructor for a class \tcode{D},
+\tcode{F2} is a constructor for a base class \tcode{B} of \tcode{D}, and
+for all arguments
+the corresponding parameters of \tcode{F1} and \tcode{F2} have the same type.
+\begin{example}
+\begin{codeblock}
+struct A {
+  A(int = 0);
+};
+
+struct B: A {
+  using A::A;
+  B();
+};
+
+int main() {
+  B b;  // OK, \tcode{B::B()}
+}
+\end{codeblock}
+\end{example}
+or, if not that,
+
 \item
 \tcode{F1} is generated from a
 \grammarterm{deduction-guide}~(\ref{over.match.class.deduct})