+* Modification times of PAX extended headers.
+
+Modification times in the ustar header blocks for the
+extended headers are set to the mtimes of the corresponding archive
+members. This can be overridden by the
+
+ --pax-opion='exthdr.mtime=STRING'
+
+command line option. The STRING is either the number of seconds since
+the Epoch or a `Time reference' (see below).
+
+Modification times in the ustar header blocks for the 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 the 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, the value 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
+