gistfile1.php

<?php

// in the validation rule
....
 'content' => array(
            'requiredConditional' => array(
                'rule' => array('requiredConditionalFieldOrValue', 'type-interaction', 'announcement', 'question-answer', 'question-answer-keyword'),
                'message' => 'The interaction required a content.',
                ),
            'notempty' => array(
                'rule' => 'notempty',
                'message' => 'Content field cannot be empty.'
                ),
            'validApostrophe' => array(
                'rule' => array('notRegex', VusionConst::APOSTROPHE_REGEX),
                'message' => VusionConst::APOSTROPHE_FAIL_MESSAGE
                ),
            'validCustomizedContent' => array(
                'rule' => array('validCustomizeContent', VusionConst::DOMAIN_NOT_RESPONSE)
                'message' => 'noMessage'
                ),
            ),


....
   public $validateFeedback = array(
        'content' => array(
            'notempty' => array(
                'rule' => 'notempty',
                'message' => 'Content field cannot be empty.'
                ),
            'validApostrophe' => array(
                'rule' => array('notRegex', VusionConst::APOSTROPHE_REGEX),
                'message' => VusionConst::APOSTROPHE_FAIL_MESSAGE
                ),
            'validCustomizeContent' => array(
                'rule' => array('validCustomizeContent', VusionConst::DOMAIN_ALL)
                'message' => 'noMessage'
                ),
            )
        );


// now the function
    public function validCustomizeContent($field, $allowedDomain, $data)
    {
        if (isset($data[$field])) {
            preg_match_all(VusionConst::CONTENT_VARIABLE_MATCHER_REGEX, $data[$field], $matches, PREG_SET_ORDER);
            $allowed = array("domain", "key1", "key2", "keys3", "otherkey");
            foreach($matches as $match) {
                $match = array_intersect_key($match, array_flip($allowed));
                foreach ($match as $key=>$value) {
                    if (!preg_match(VusionConst::CONTENT_VARIABLE_KEY_REGEX, $value)) {
                        return __("To be used as customized content, '%s' can only be composed of letter(s), digit(s) and/or space(s).", $value);
                    }
                }
                if (!preg_match($allowedDomain, $match['domain'])) {
                    return __("To be used as customized content, '%s' can only be either: %s.", $match['domain'], implode(',', $allowedDomain));
                }
                if ($match['domain'] == 'participant') {
                    if (isset($match['key2'])) {
                        return VusionConst::CONTENT_VARIABLE_DOMAIN_PARTICIPANT_FAIL;
                    }
                } else if ($match['domain'] == 'contentVariable') {
                    if (isset($match['otherkey'])) {
                        return VusionConst::CONTENT_VARIABLE_DOMAIN_CONTENTVARIABLE_FAIL;
                    }
                } 
            }
        }
        return true;
    }