WICG
Support for reading and writing file attributes
All operating systems provide a mechanism to store and read Extended file attributes, provide an API to read/write/delete file attributes.
The attributes can store metadata such as the unique file ID (which is retained even if the file is moved), file version, mime type, checksum, contents encoding, etc.
The API could be part of the FileSystemFileHandle interface:
FileSystemFileHandle.prototype.readAttributes()FileSystemFileHandle.prototype.readAttribute(name)FileSystemFileHandle.prototype.writeAttribute(name, value)FileSystemFileHandle.prototype.deleteAttribute(name)
It doesn't seem that you are coming from a solid understanding of the topic. "Extended file attributes" is umbrella term for a host of implementations which vary wildly across filesystems. Corresponding APIs are not necessarily being part of operating systems. Speaking of the most widely used desktop OS, Windows doesn't have API for working with NTFS extended attributes. You need to use low-level filesystem calls or resort to external libraries.
What you are suggesting is a thick cross-platform abstraction layer that will have to be implemented in multiple browsers. I very much doubt that anyone will subscribe to this.
APIs are different on all OSes, but all OSes and their most popular file system support file attributes.
Clipboard API is also different on all systems, but all browsers support them.
but all OSes and their most popular file system support file attributes
This is simply not true. As I already noted, Windows itself knows nothing about NTFS extended attributes.
Clipboard API is also different on all systems, but all browsers support them.
Arguments like these don't make sense. The amount of implementation effort is incommensurate.