This package implements the main user interface of Magit — the collapsible sections that make up its buffers. This package used to be distributed as part of Magit but how it can also be used by other packages that have nothing to do with Magit or Git.
To learn more about the section abstraction and available commands and user options see (magit)Sections. This manual documents how you can use sections in your own packages.
When the documentation leaves something unaddressed, then please consider that Magit uses this library extensively and search its source for suitable examples before asking me for help. Thanks!