A slideout modal is a panel that slides in above the main view, making the underlying content partially visible. The purpose is being able to show a large amount of additional content and not interrupting the primary task.
Use a slideout modal to allow a user to reference information from the main view, maintaining a contextual connection to the actual task. Whilst this is a great enabler from desktop, the slideout modal covers the whole mobile viewport in order to make better use of the available space.
This behaviour is recommended to use for tasks such as; filtering of main content and show item details instead of expanding a row.
It should slide into position in the viewport from the right partially covering the main content for desktop, whilst in mobile covering the whole viewport.
Above: Slide-out example in Morning
Above: Slide-out example in RPD Alison