Custom libraries make working with your own graphics and icons a breeze. You can quickly and easily import your own libraries and use your custom shapes. Alternatively, you can create a custom library from an existing diagram, as you will learn how to do in this exercise.
New release adds scratchpad in Chrome App https://support.draw.io/questions/10420280
How to use the scratchpad in an Entity Relationship Diagram (ERD) to copy and automatically link complex container shapes in draw.io.