Star is a new, modern, and simple archive format. Star is meant to be used as a cross-platform archiving file format. Because of the simplicity of the file format, star can be used by mainstream OS's and embedded systems alike.
If you want to read more about star, go check out the whitepaper.
The star file format is simple and secure. It begins with a filelist with the SHA-256 hash of the contents. Each archive, or 'starfile,' contains the full contents of each file. It does not, however, store any OS-specific information like permissions, ownership, or locks
If you want to view the file specification, you can read it in the docs.