The regular expression query in $in is not working. It works fine in the mongo shell.
Does not work:
OpMatch := bson.M{"$match": bson.M{"wordname": bson.M{"$in": [...]string{"/^how$/"}}}}
Works:
OpMatch := bson.M{"$match": bson.M{"wordname": bson.M{"$in": [...]string{"how"}}}}