+
+ <para>Optionally, if prefixed with
+ <literal>~</literal>, the access mode is masked
+ based on the already set access bits for
+ existing file or directories: if the existing
+ file has all executable bits unset, all
+ executable bits are removed from the new
+ access mode, too. Similarly, if all read bits
+ are removed from the old access mode, they will
+ be removed from the new access mode too, and
+ if all write bits are removed, they will be
+ removed from the new access mode too. In
+ addition, the sticky/SUID/SGID bit is removed unless
+ applied to a directory. This
+ functionality is particularly useful in
+ conjunction with <varname>Z</varname>.</para>