While we plan to release more options to delete your documents (e.g. by query), for the starter you can delete documents by their _id. To delete documents by their _id, you can pass a list of _ids to the delete() function: 
client.collection("books").delete(
    ["book-1", "book-2", "book-3"]
)
If the documents are too large it can take a while until the deletion process is complete. To check the status of the deletion, query the document again.