[namespace.udecl] Clarify error in example. (#1254)

Author: jensmaurer

source/declarations.tex

@@ -3055,12 +3055,15 @@
 member function, then all functions named shall be accessible. The base
 class members mentioned by a \grammarterm{using-declarator} shall be
 visible in the scope of at least one of the direct base classes of the
-class where the \grammarterm{using-declarator} is specified. \begin{note}
+class where the \grammarterm{using-declarator} is specified.
+
+\pnum
+\begin{note}
 Because a \grammarterm{using-declarator} designates a base class member
 (and not a member subobject or a member function of a base class
 subobject), a \grammarterm{using-declarator} cannot be used to resolve
-inherited member ambiguities. For example,
-
+inherited member ambiguities.
+\begin{example}
 \begin{codeblock}
 struct A { int x(); };
 struct B : A { };
@@ -3074,9 +3077,10 @@
   int x(double);
 };
 int f(D* d) {
-  return d->x();    // ambiguous: \tcode{B::x} or \tcode{C::x}
+  return d->x();    // error: overload resolution selects \tcode{A::x}, but \tcode{A} is an ambiguous base class
 }
 \end{codeblock}
+\end{example}
 \end{note}
 
 \pnum