Insert a multi-element container that can be expanded/collapsed.
Inserts a container into your app that can be used to hold multiple elements and can be expanded or collapsed by the user. When collapsed, all that is visible is the provided label.
To add elements to the returned container, you can use "with" notation (preferred) or just call methods directly on the returned object. See examples below.
Currently, you may not put expanders inside another expander.
A string to use as the header for the expander.
If True, initializes the expander in "expanded" state. Defaults to False (collapsed).