All options prefixed with "X-" are interpreted as comments or as userspace application-specific options. These options are not stored in user space (e.g., _mtab_ file), nor sent to the mount._type_ helpers nor to the *mount*(2) system call. The suggested format is **X-**__appname__._option_.
*x-**::
-The same as *X-** options, but stored permanently in user space. This means the options are also available for *umount*(8) or other operations. Note that maintaining mount options in user space is tricky, because it's necessary use libmount-based tools and there is no guarantee that the options will be always available (for example after a move mount operation or in unshared namespace).
+The same as *X-** options, but stored permanently in user space. This means the options are also available for *umount*(8) or other operations. Note that maintaining mount options in user space is tricky, because it's necessary to use libmount-based tools and there is no guarantee that the options will be always available (for example after a move mount operation or in unshared namespace).
+
Note that before util-linux v2.30 the x-* options have not been maintained by libmount and stored in user space (functionality was the same as for X-* now), but due to the growing number of use-cases (in initrd, systemd etc.) the functionality has been extended to keep existing _fstab_ configurations usable without a change.