帮忙看下这个代码里面的echo "<b><u>";这个是什么意思？

Question

<?PHP
date_default_timezone_set('PRC');
$today = time();
$year =$_GET["year"];
$month =$_GET["month"];
if($year=='') $year = date("Y",$today);
if($month=='') $month = date("m",$today);
if((int)$month==0){$year-=1;$month=12;}
$time = mktime(0,0,0,$month,1,$year);
$year = date('Y',$time);
$month = date('m',$time);
echo "<table width=240 cellspacing=0 cellpadding=0>";
echo "<tr><td colspan=7 class=title>";
$str   = "<a href=?year=".($year-1)."&month=".$month.">";
$str .= "&laquo;</a> ".$year."年 ";
$str .= "<a href=?year=".($year+1)."&month=".$month.">";
$str .= "&raquo;</a>   ";
$str .= "<a href=?year=".$year."&month=".($month-1).">";
$str .= "&laquo;</a> ".$month."月 ";
$str .= "<a href=?year=".$year."&month=".($month+1).">";
$str .= "&raquo; </a>";
echo $str;
echo "</td></tr>";
echo     "<tr>";
$str  = "<td>一</td>";
$str .= "<td>二</td>";
$str .= "<td>三</td>";
$str .= "<td>四</td>";
$str .= "<td>五</td>";
$str .= "<td>六</td>";
$str .= "<td>七</td>";
echo $str;
echo "</td>";
$days = date('t',$time);
$fstdw = date('N',$time);
$rows = ceil(($days + $fstdw-1)/7);
$cd = 1;
for($i=0;$i<$rows;$i++){
   echo "<tr>";
   for($j=0;$j<7;$j++){
       echo "<td>";
       if($cd >= $fstdw && $cd<$days+$fstdw){
           $oday = $cd-$fstdw+1;
           if($oday==date('d',time()))
               echo "<b><u>";//这里是什么意思
           echo ($cd-$fstdw+1);
       }else{
           echo " ";
       }
       $cd++;
       echo "</td>";
   }
   echo "</tr>";
}
echo "</table>";
?>

Answer 1

HTML标签，b加重，u，有点不清楚了