- The value after attribute type <literal>7</literal> is
- <literal>1</literal> (=ascending), or <literal>2</literal>
- (=descending).
- The attributes+term (APT) node is separate from the rest of the
- PQF query, and must be <literal>@or</literal>'ed.
- The term associated with this attribute is the sorting level,
- where
- <literal>0</literal> specifies the primary sort key,
- <literal>1</literal> the secondary sort key, and so on.
+ A sorting subquery needs two attributes: an index (such as a
+ BIB-1 type-1 attribute) specifying which index to sort on, and a
+ type-7 attribute whose value is be <literal>1</literal> for
+ ascending sorting, or <literal>2</literal> for descending. The
+ term associated with the sorting attribute is the priority of
+ the sort key, where <literal>0</literal> specifies the primary
+ sort key, <literal>1</literal> the secondary sort key, and so
+ on.