 to the
property map's key type. Details of that conversion are unspecified.
2) The object passed as the value must be convertible to the
property map's value type. Details of that conversion are unspecified.
3) The property map need not support this member function, in which
case an error will be signaled.  This is the runtime analogue of the
Readable Property Map concept.</p>
<pre class="literal-block">
const std::type_info&amp; key() const
</pre>
<p>Returns a <tt class="docutils literal"><span class="pre