</span> <span class="identifier">ChannelT</span><span class="special">,</span> <span class="identifier">SeverityT</span><span class="special">,</span> <span class="identifier">fallback_to_none</span><span class="special">,</span> <span class="identifier">SeverityFallbackT</span><span class="special">,</span> <span class="identifier">ChannelOrderT</span><span class="special">,</span> <span class="identifier">SeverityCompareT</span><span class="special">,</span> <span class="identifier">use_std_allocator</spa