public function getFieldAnnotationsForMatchingTag($tag, $fieldName = null) {

        if ($fieldName) {
            return isset($this->fieldAnnotations[$fieldName][$tag]) ? $this->fieldAnnotations[$fieldName][$tag] : array();
        } else {

            $matchingAnnotations = array();
            foreach ($this->getFieldAnnotations() as $field => $fieldAnnotations) {
                if (isset($fieldAnnotations[$tag])) {
                    $matchingAnnotations[$field] = $fieldAnnotations[$tag];
                }
            }

            return $matchingAnnotations;

        }
    }