Description of the JSON in menu.d and acl.d?

Are there any written descriptions about the JSON options in /usr/share/luci/menu.d. /usr/share/rpcd/acl.d/ and /usr/share/acl.d?

It looks like the LuCi top level menu bar is drawn based on the contents of the file menu.d/luci-base.json. Is that specific file always processed first, and then the other JSON files in the same directory? Is this described anywhere?

Thanks!