拆分为数组，难点是 C(x, y("z", 2, 0)), 是一个整体。

$s='A, B, C(x, y("z", 2, 0)), D, E';$keywords = preg_split("/\,\s(?=[A-Z])/", $s);var_dump($keywords);

$s='A, B, C(x, y("z", 2, 0)), D, E';$keywords = preg_split("/\,\s(?=[A-Z])/", $s);var_dump($keywords);

$s='A, B, C(X, Y("Z", 1, 0)), D(X, Y("Z", 2, 0)), E,F(X, Y("Z", 3, 0))';//提取获取里面的内容preg_match_all("/\(.*?\)\)/",$s,$match);//这部分正则可以自行修改$s = str_replace($match[0],'%',$s);//将整体的替换成某个符合,%百分号也可以自己选定$exs = explode(',',$s);$i = 0;foreach($exs as $key=>$value){	if (strpos($value,"%") !== false) {				$exs[$key] = str_replace('%',$match[0][$i],$value);		$i ++;	}}var_dump($exs);

$s='A, B, C(x, Y("z", 2, 0)), D, E';print_r(foo($s));function foo($s) {  $r = array();  $m = 0;  $t = '';  for($i=0; $i<strlen($s); $i++) {    if($s{$i} == '(') $m++;    if($s{$i} == ')') $m--;    if($m == 0 && $s{$i} == ',') {      if($t) $r[] = $t;      $t = '';    }else $t .= $s{$i};  }  if($t) $r[] = $t;  return $r;}

Array(    [0] => A    [1] =>  B    [2] =>  C(x, Y("z", 2, 0))    [3] =>  D    [4] =>  E)