<?php
    $string = 'xyz123abc';
    $parts = preg_split("/(,?\s+)|(\w\d)|(\d\w)/", $string);
    var_dump ($parts);

    $string = '19yo';
    $parts = preg_split("/(,?\s+)|(\w\d)|(\d\w)/", $string);
    var_dump ($parts);

    $string = 'xyz123';
    $parts = preg_split("/(,?\s+)|(\w\d)|(\d\w)/", $string);
    var_dump ($parts);
?>

array(3) {
  [0]=>
  string(2) "xy"
  [1]=>
  string(0) ""
  [2]=>
  string(3) "abc"
}
array(2) {
  [0]=>
  string(0) ""
  [1]=>
  string(2) "yo"
}
array(3) {
  [0]=>
  string(2) "xy"
  [1]=>
  string(0) ""
  [2]=>
  string(0) ""
}