title: Example of ill-formed implicit conversion
body: <p><code>N3797::13.3.3.1/2 [over.best.ics]</code> tells about an ill-formed implicit conversion as follows:</p>
  
  <blockquote>
    <p>Implicit conversion sequences are concerned only with the type,
    cv-qualification, and value category of the argument and how these are
    converted to match the corresponding properties of the parameter.
    Other properties, such as the lifetime, storage class, alignment, or
    accessibility of the argument and whether or not the argument is a
    bit-field are ignored. So, although an implicit conversion sequence
    can be defined for a given argument-parameter pair, <em>the conversion</em>
    from the argument to the parameter <em>might still be ill-formed</em> in the
    final analysis.</p>
  </blockquote>
  
  <p>I have no idead about how can we ever define such a conversion. The thing is all kind of conversions I know are well-formed conversion like user-defined conversion with <code>operatorn A(){ ... }</code>  or a standard conversion. Couldn't you provide an example of the ill-formed conversion?</p>