bson/src/main/org/bson/AbstractBsonWriter.java
public void pipe(final BsonReader reader, final List<BsonElement> extraElements) {
        notNull("reader", reader);
        notNull("extraElements", extraElements);
        pipeDocument(reader, extraElements);
    }
public void pipe(final BsonReader reader, final List<BsonElement> extraElements) {
        notNull("reader", reader);
        notNull("extraElements", extraElements);
        pipeDocument(reader, extraElements);
    }
Reads a single document from the given BsonReader and writes it to this, appending the given extra elements to the document.

@param reader the source of the document
@param extraElements the extra elements to append to the document
@since 3.6