Format string. $value expands to the field value, and $name expands to the field name, $title to the field title, $form to the name of the form the field is in. The standard format tokens are also expanded.
Specifiy a revision of the topic. If not specified, defaults to the most recent rev (or the viewed rev if viewing an old rev of the same topic)
Text shown if the field is defined in the topic, but the field value is empty. For example, a text field for which all the content has been deleted.
Text shown if the field is not defined in the topic (even if it is specified in the form definition). For example, this is used when a field exists in the form definition, but the referring topic hasn't been edited since it was added.