帮忙看下这个代码里面的echo "<b><u>";这个是什么意思？

Question

<?PHPdate_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