Message
Element <ack/> may only contain <title/> and <p/> elements.
Rule XPath:
This rule REPORTS an alert when the following is TRUE:
*[not(self::title or self::p)]Element <ack/> may only contain <title/> and <p/> elements.
This rule REPORTS an alert when the following is TRUE:
*[not(self::title or self::p)]