The Structured Query request must aggregate the results of the individual queries into a final results list, using
the retrieved index items. However, the aggregation is not performed in a single manner, but is controlled by
operators on each individual query, using the following attribute.
The op value can be required, which means that the index items of the final results must have individual results
from this query. The op value can be negative, which means that the index items of the final results must not have
individual results from this query. The op value can be optional, which means that the index items of the final
results are not required to have individual results from this query. The default value is optional. Note that
required queries should be executed first, then optional queries, then negative queries in order for the
aggregation to work properly.
See
SearchPropertyEditors.