$re = '/(\'[^\']*?(?:\\\\\'[^\']*?)*\'|[^\s]+)/i';
$str = 'Discerning between \'the single quote\\\'s double purpose\' as a \'quote marker\', like ", and a \'a cotraction\\\'s marker.\'.
If you asked the author and he was speaking in the third person, he would say \'CFQueryParam\\\'s example is contrived, and he knew that but he had the world\\\'s most difficult time thinking up an example.\'';
$subst = "**`$1`**,";
$result = preg_replace($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