--Inserted documents should be compared to the partialFilterExpression respecting the index's collation.
--Index selection for partial indexes should use collation-aware comparison of the query and the partialFilterExpression.

With respect to collation, a partial index may be used anywhere that an index is used. If the query contains string comparison, then we already require that the query and index collators match. If the query does not contain string comparison, then no collator is needed to compare the query to the partialFilterExpression.