Use case

Many other frameworks come with this feature out of the box. There are 5 packages that provide sticky headers, none of which work properly in a CustomScrollView with a center key on a Sliver (sticky_headers doesn't even work with CustomScrollView). Each tries to make up for the failings of the other.

https://pub.dev/packages/flutter_sticky_header
https://pub.dev/packages/sticky_headers
https://pub.dev/packages/sticky_and_expandable_list
https://pub.dev/packages/sticky_infinite_list
https://pub.dev/packages/sticky_and_expandable_list

Proposal

SliverPersistantHeader really should have a property (sticky) that allows for sticky headers.