Based on code sample originally posted by "Anonymous" on 2005年12月14日. The /e modifier is no longer supported by preg_replace(). Rewritten to use preg_replace_callback() instead. Tested with PHP 7.3.
The function below will standardize the capitalization on people's names, addresses, and the titles of reports and essays . Adapt the lists in "$all_uppercase" and "$all_lowercase" to suit the data that you are working with.
function ucwords_title($string, $is_name = false) {
 // Exceptions to standard case conversion
 if ($is_name) {
 $all_uppercase = '';
 $all_lowercase = 'De La|De Las|Der|Van De|Van Der|Vit De|Von|Or|And';
 } else {
 // Addresses, essay titles ... and anything else
 $all_uppercase = 'Us|Ca|Mx|Po|Rr|Se|Sw|Ne|Nw';
 $all_lowercase = 'A|And|As|By|In|Of|Or|To';
 }
 $prefixes = 'Mac|Mc';
 $suffixes = "'S";
 // Trim whitespace and convert to lowercase
 $str = strtolower(trim($string));
 // Capitalize all first letters
 $str = preg_replace_callback('/\\b(\\w)/', function ($m) {
 return strtoupper($m[1]);
 }, $str);
 if ($all_uppercase) {
 // Capitalize acronyms and initialisms (e.g. PHP)
 $str = preg_replace_callback('/\\b(' . $all_uppercase . ')\\b/', function ($m) {
 return strtoupper($m[1]);
 }, $str);
 }
 if ($all_lowercase) {
 // Decapitalize short words (e.g. and)
 if ($is_name) {
 // All occurrences will be changed to lowercase
 $str = preg_replace_callback('/\\b(' . $all_lowercase . ')\\b/', function ($m) {
 return strtolower($m[1]);
 }, $str);
 } else {
 // First and last word will not be changed to lower case (i.e. titles)
 $str = preg_replace_callback('/(?<=\\W)(' . $all_lowercase . ')(?=\\W)/', function ($m) {
 return strtolower($m[1]);
 }, $str);
 }
 }
 if ($prefixes) {
 // Capitalize letter after certain name prefixes (e.g 'Mc')
 $str = preg_replace_callback('/\\b(' . $prefixes . ')(\\w)/', function ($m) {
 return $m[1] . strtoupper($m[2]);
 }, $str);
 }
 if ($suffixes) {
 // Decapitalize certain word suffixes (e.g. 's)
 $str = preg_replace_callback('/(\\w)(' . $suffixes . ')\\b/', function ($m) {
 return $m[1] . strtolower($m[2]);
 }, $str);
 }
 return $str;
}
// A name example
print ucwords_title("MARIE-LOU VAN DER PLANCK-ST.JOHN", true);
// Output: Marie-Lou van der Planc-St.John
// A title example
print ucwords_title("to be or not to be");
// Output: "To Be or Not to Be"