问下这种PHP写法什么意思，关于字符串的

 if(!empty($attribute)) {foreach($attribute as $v){ $str.=",{$v}";} } $str.=",";

$attribute = array(1,2,3,0,0,5,'', 'A');$str = '';if(!empty($attribute)) {  foreach($attribute as $v) {    $v and $str.=",{$v}";  }}$str and $str.=",";echo $str;

$attribute = array(1,2,3,0,0,5,'', 'A');$str = '';if(!empty($attribute)) {  foreach($attribute as $v) {    $str.=",{$v}";  }}$str.=",";echo $str;

if(!empty($attribute)){	foreach($attribute as $v){		$v and $str.=",{$v}";	} }$str and $str.=",";

if(!empty($attribute)){	foreach($attribute as $v){		if($v){			$str.=",".$v;		}	}}if($str){	$str.=",";}

$str || $str=“缺省值”;