Register snippet : validate a select list value

<label for="activity">Activité
<select name="activity:validFormActivity" id="activity" title="[[+error.activity]]" >
  <option value="[[+customFields.activity]]">[[+customFields.activity]]</option>
  <option value="1">Hotesse</option>
  <option value="2">Agent d'accueil</option>
  <option value="3">Mannequin</option>
  <option value="4">Steward</option>
</select>

<?php

    global $modx;
    global $scriptProperties;
    $tmp = $scriptProperties ['value'] ;

    if ( (int ) $tmp > 0 ) {
             
        $modx->setPlaceholders( array ('activity' => $tmp ), 'customFields.' );  

    } else {

        return 'choose an option.<br />';

    }

    return true;

?>

 <label for="otheractivity">Autre activité ( précisez )
        <input type="text" name="otheractivity:validFormOtheractivity" id="otheractivity" value="[[+otheractivity]]"  
 title="[[+error.otheractivity]]" />
        </label>

<?php
    
    global $modx;

    global $scriptProperties;

    $tmp =  $scriptProperties ['value'] ;

    if ( strlen ( $tmp ) < 30 ) {

        $modx->setPlaceholders( array ('otheractivity' =>'rrr'. $tmp ), 'customFields.' );  

    } else {

        return '30 chars max<br />';

    }


    return true;

?>

<?php
$tmp = $scriptProperties['value'];
if (strlen($tmp) < 30) {
    $modx->setPlaceholders(array('otheractivity' =>'rrr'. $tmp ), 'customFields.' );
} else {
    $scriptProperties['validator']->errors[$scriptProperties['key']] = '30 chars max<br />';
    return false;
}
return true;