, then the symbol table generator
            will use the first element stored in that container as the key to be
            used for lookup. The <code class="computeroutput"><span class="identifier">value_type</span></code>
            (returned by <a class="link" href="../../../advanced/customize/store_value/container_value.html" title="Determine the Type to be Stored in a Container (Qi)"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="ident