This API is provided as a preview for developers and may change based on feedback that we receive. Do not use this API in a production environment.
Index where to place the new section
readonly index: RelativeIndex;
Index is zero-based and for convenience index -1 means place new section at the end. 0 means place new section at the beginning. Both 0 and -1 and can be used when inserting the first section into and empty layout.