php截取字符串中的关键字，并高亮显示

<?php
$str = "hahaceshi测试一下关键字高亮显示，以及长字符串截取的问题！";
$key = "关键字";$r = sub_key_h($str,$key);
echo $r;function sub_key_h($str,$key,$len=10,$enc='utf-8'){
$strlen = mb_strlen($str,$enc);
$keylen = mb_strlen($key,$enc);
$keypos = mb_strpos($str,$key,0,$enc);
$leftpos = $keypos - 1;
$rightpos = $keypos + $keylen; if($keylen > $len){
return "<font style='font-color:red;'>".mb_substr($key,0,$len,$enc)."</font>...";
}
$result = "<font style='font-color:red;'>".$key."</font>";
for($i = 0;$i<$len - $keylen;$i++){
if($leftpos >= 0){
$result = mb_substr($str,$leftpos--,1,$enc).$result;
}else{
$result .= mb_substr($str,$rightpos++,1,$enc);
}
}
if($leftpos >= 0){
$result = "...".$result;
}
if($rightpos < $strlen){
$result .= "...";
}
return $result;
}
?>

...shi测试一下<font style='font-color:red;'>关键字</font>...