span> <span class="identifier">string_type</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span> <span class="identifier">iterator</span><span class="special">,</span> <span class="keyword">bool</span> <span class="special">&gt;</span> 
  <a class="link" href="basic_environment.html#idp51500144-bb"><span class="identifier">e