s=keyword>struct</span> <span class=identifier>record_year</span>
<span class=special>{</span>
  <span class=comment>// result_type typedef required by Key Extractor concept</span>
  <span class=keyword>typedef</span> <span class=identifier>boost</span><span class=special>::</span><span class=identifier>gregorian</span><span class=special>::</span><span class=identifier>greg_year</span> <span class=identifier>result_type</span><span class=special>;</span> 
  
  <span class=identifier>result_type</span> <spa