current inner tuple */
    bool        allTheSame;     /* tuple is marked all-the-same? */
    bool        hasPrefix;      /* tuple has a prefix? */
    Datum       prefixDatum;    /* if so, the prefix value */
    int         nNodes;         /* number of nodes in the inner tuple */
    Datum      *nodeLabels;     /* node label values (NULL if none) */
} spgInnerConsistentIn;

typedef struct spgInnerConsistentOut
{
    int         nNodes;         /* number of child nodes to be visited */
    int        *nodeNumbers;    /* their indexes in the node array */
    int        *levelAdds;      /* increment level by this much for each */
    Datum      *reconstructedValues;    /* associated reconstructed values */
    void      **traversalValues;        /* opclass-specific traverse values */
    double    **distances;              /* associated distances */
} spgInnerConsistentOut;
</programlisting>

       The array <structfield>scankeys</structfield>, of length <structfield>nkeys</structfield>,
       describes the index search condition(s).  These conditions are
       combined with AND &mdash; only index entries that satisfy all of
       them are interesting.  (Note that <structfield>nkeys</structfield> = 0 implies
       that all index entries satisfy the query.)  Usually the consistent
       function only cares about the <structfield>sk_strategy</structfield> and
       <structfield>sk_argument</structfield> fields of each array entry, which
       respectively give the indexable operator and comparison value.
       In particular it is not necessary to check <structfield>sk_flags</structfield> to
       see if the comparison value is NULL, because the SP-GiST core code
       will filter out such conditions.
       The array <structfield>orderbys</structfield>, of length <structfield>norderbys</structfield>,
       describes ordering operators (if any) in the same manner.
       <structfield>reconstructedValue</structfield> is the value reconstructed for the
       parent tuple; it is <literal>(Datum) 0</literal> at the root level or if the
       <function>inner_consistent</function> function did not provide a value at the
       parent level.
       <structfield>traversalValue</structfield> is a pointer to any traverse data
       passed down from the previous call of <function>inner_consistent</function>
       on the parent index tuple, or NULL at the root level.
       <structfield>traversalMemoryContext</structfield> is the memory context in which
       to store output traverse values (see below).
       <structfield>level</structfield> is the current inner tuple's level, starting at
       zero for the root level.
       <structfield>returnData</structfield> is <literal>true</literal> if reconstructed data is
       required for this query; this will only be so if the
       <function>config</function> function asserted <structfield>canReturnData</structfield>.
       <structfield>allTheSame</structfield> is true if the current inner tuple is
       marked <quote>all-the-same</quote>; in this case all the nodes have the
       same label (if any) and so either all or none of them match the query
       (see <xref linkend="spgist-all-the-same"/>).
       <structfield>hasPrefix</structfield> is true if the current inner tuple contains
       a prefix; if so,
       <structfield>prefixDatum</structfield> is its value.
       <structfield>nNodes</structfield> is the number of child nodes contained in the
       inner tuple, and
       <structfield>nodeLabels</structfield> is an array of their label values, or
       NULL if the nodes do not have labels.
      </para>

      <para>
       <structfield>nNodes</structfield> must be set to the number of child nodes that
       need to be visited by the search, and
       <structfield>nodeNumbers</structfield> must be set to an array of their indexes.
       If the operator class keeps track of levels, set
       <structfield>levelAdds</structfield> to an array of the level increments