s="computeroutput"><span class="identifier">mapped</span>
          <span class="identifier">type</span></code> corresponding to the key.
          Otherwise, inserts the new value at the end as if by insert, constructing
          it from <code class="computeroutput"><span class="identifier">value_type</span><span class="special">(</span><span class="identifier">key</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span>