Required Metadata for Omeka plugin work

RequiredMetadataPlugin.php

<?php
class RequiredMetadataPlugin extends Omeka_Plugin_AbstractPlugin
{
    
    protected $_hooks = array('before_save_item');
    protected $_filters = array(
       'itemTitleLengthValidator' => array('Validate', 'Item', 'Dublin Core', 'Title'),
    );
    
    public function hookBeforeSaveItem($args)
    {
        $item = $args['record'];
        $title = metadata($item, array('Dublin Core', 'Title'));
        if(empty($title)) {
            $item->addError("DC Title", 'DC Title cannot be empty!');
        }
    }
    
    
    public function itemTitleLengthValidator($isValid, $args)
    {
      $record = $args['record'];
      $text = $args['text'];
      if(strlen($text) < 10 ) {
          $record->addError('DC Title Length', 'DC Title is Too Short!');
          return false;
      }
      return true;
    }
    
}

The first param to addError will always have a unique value, so repeated us of 'Title' there will clobber later usage. It doesn't come out especially pretty on the admin side, but it might do the job, to just use more descriptive text instead of the real field name.