Dear Maintainer,

tune2fs documents the -E switch as:

   Extended options are comma separated, and may take an  argu‐ ment using the equals ('=') sign.

and the mount_opts sub-option:

   mount_opts=mount_option_string
      mount_option_string is an arbitrary string with a maximum length  of  63  bytes...

The problem is that mount options are also comma-separated and tune2fs
does not seem to support this (instead assuming the comma separates
-E options), therefore, the string is not arbitrary, or at least, its
impossible to specify arbitrary contents, or, if it is possible, its
undocumented how to do so.

I don't know if this is a documentation problem or not, but it would be
nice if one could actually specify an arbitrary mount_option_string with
tune2fs.