The OpenChemLib fragment fingerprint is compatible with all of the provided query features and therefore can be used for the prefiltering during substructure search. When using query features for the search in combinatorial libraries, for computing the connector region heuristic we do remove all narrowing query features, as they may incorrectly filter out candidate synthons, e.g. when one of the terminal atoms of the connector region has a query feature that requires it to contain a specific number of neighbors.