specified, it will inherit from the 
  base parser class which typedefs its parser_category_t as <tt>plain_parser_category</tt>. 
  Some template classes are provided to distinguish different types of parsers. 
  The following categories are the most generic. More specific types may inherit 
  from these.</p>
<table width="90%" border="0" align="center">
  <tr> 
    <td colspan="2" class="table_title">Parser categories</td>
  </tr>
  <tr> 
    <td class="table_cells" width="33%"><tt>plain_parser_category</t