s="keyword">typedef</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span>                         <a name="boost.xpressive.basic_regex.string_type"></a><span class="identifier">string_type</span><span class="special">;</span>  
  <span class="keyword">typedef</span> <span class="identifier">regex_constants</span><span class="special">::</span><span class="identifier">syntax_option_type</span> <a name="boost.xpressive.basic_regex.flag_type"></a><span class="identifier">fla