$re = '/(?:
(?:["“][^"”]*[.?!]["”])
|(?:(?:
["“][^"”]*(?<![.?!])["”]
|[^".?!]+
)+)[.?!]["”]?
)
\K\s*/mx';
$str = '"This is," she said, "a bad idea."
“Beer. Whatever you’ve got on draft is fine.” He handed my a bottle. I didn\'t want that.
';
$subst = "\n";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php