+See Tar Manual, section 3.9 "Controlling Warning Messages", for a
+detailed discussion.
+
+* New command line option `--level'
+
+The `--level=N' option sets the incremental dump level N. It
+is valid when used in conjunction with the -c and --listed-incremental
+options. So far the only meaningful value for N is 0. The
+`--level=0' option forces creating the level 0 dump, by truncating
+the snapshot file if it exists.
+
+* Files removed during incremental dumps
+
+If a file or directory is removed while incremental dump is
+in progress, tar exact actions depend on whether this file
+was explicitly listed in the command line, or was found
+during file system scan.
+
+If the file was explicitly listed in the command line, tar
+issues error message and exits with the code 2, meaning
+fatal error.
+
+Otherwise, if the file was found during the file system scan,
+tar issues a warning, saying "File removed before we read it",
+and sets exit code to 1, which means "some files differ".
+If the --warning=no-file-removed option is given, no warning
+is issued and exit code remains 0.
+
+* Modification times of PAX extended headers.
+
+Modification times in ustar header blocks of extended headers
+are set to mtimes of the corresponding archive members. This
+can be overridden by the
+
+ --pax-opion='exthdr.mtime=STRING'
+
+command line option. The STRING is either number of seconds since
+the Epoch or a `Time reference' (see below).
+
+Modification times in ustar header blocks of global extended
+headers are set to the time when tar was invoked.
+
+This can be overridden by the
+
+ --pax-opion='globexthdr.mtime=STRING'
+
+command line option. The STRING is either number of seconds since
+the Epoch or a `Time reference' (see below).
+
+* Time references in --pax-option argument.
+
+Any value from the --pax-option argument that is enclosed in a pair
+of curly braces represents a time reference. The string between the
+braces is understood either as a textual time representation, as described in
+chapter 7, "Date input formats", of the Tar manual, or as a name of
+an existing file, starting with `/' or `.'. In the latter
+case, it is replaced with the modification time of that file.
+
+* Environment of --to-command script.
+
+The environment passed to the --to-command script is extended with
+the following variables:
+
+ TAR_VERSION GNU tar version number
+ TAR_ARCHIVE The name of the archive
+ TAR_VOLUME Ordinal number of the volume
+ TAR_FORMAT Format of the archive
+ TAR_BLOCKING_FACTOR Current blocking factor
+