 <a class="link" href="category.html#idm14158-bb">public member functions</a></span>
  <span class="identifier">index_type</span> <a class="link" href="category.html#idm14159-bb"><span class="identifier">index</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&amp;</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
  <span class="i