Description:

attr-devel contains the libraries and header files needed to
develop programs which make use of extended attributes. This
interface is compatible with the SGI IRIX extended attribute
interface, and makes use of an unofficial Linux system call.

Currently only XFS is supported, and the (experimental, unofficial)
system call interface is likely to change in the future. However,
the API built above this system call is unlikely to change and is
used by programs such as xfsdump(8), xfsrestore(8) and xfs_fsr(8).

You should install attr-devel if you want to develop programs
which make use of extended attributes. If you install attr-devel,
you'll also want to install attr.