 a_ios<span class="special">,</span> <span class="keyword">const</span> <span class="identifier">period_type</span> <span class="special">&amp;</span><span class="special">,</span> 
                         <span class="keyword">const</span> <span class="identifier">duration_type</span> <span class="special">&amp;</span> dur_unit<span class="special">,</span> 
                         <span class="keyword">const</span> <span class="identifier">facet_type</span> <span class="special">&amp;</span> facet<span 