Initial summary (a co-constraint use case)

source: FV

   An envelope fragment has a header and a body containing several subelements of
   different types. The header contains an element detailing the number of
   elements, by type. Of course, numbers must match with actual elements. E.g.:

    <minutes>
        <header>
            <date>... </date>
            ...
            <items>
                <approved>3</approved>
                <postponed>1</postponed>
                ...
            </items>
        </header>
        <body>
            <act status="approved">
                ...
            </act>
            <act status="approved">
                ...
            </act>
            <act status="postponed">
                ...
            </act>
            <act status="approved">
                ...
            </act>
        </body>
    </minutes>