LD&#34; and &#34;SHOULD NOT&#34; are appropriate when valid exceptions to a
    general requirement are known to exist or appear to exist, and it is
    infeasible or impractical to enumerate all of them.  However, they
    should not be interpreted as permitting implementors to fail to
    implement the general requirement when such failure would result in
    interoperability failure.

<span><a name="section-3" href="#section-3">3</a>. Storage model</span>

    The server stores data in nodes that form a 