piklist-filter-piklist_validation_rules

<?php

  add_filter('piklist_validation_rules', 'check_valid_number', 11);
  function check_valid_number($validation_rules)
  {
    $validation_rules['my_number'] = array(
      'rule' => "/[-+]?[0-9]*[.,]?[0-9]+/"
      ,'message' => __('is not a number')
    );
   
    return $validation_rules;
  }