+.RS 4
+.TP 4
+.B batch-tag
+
+The default
+.B batch-tag
+dump format is intended to more robust against malformed message-ids
+and tags containing whitespace or non-\fBascii\fR(7) characters.
+Each line has the form
+
+.RS 4
+.RI "+<" "encoded-tag" "> " "" "+<" "encoded-tag" "> ... -- " "" " id:<" quoted-message-id >
+
+Tags are hex-encoded by replacing every byte not matching the regex
+.B [A-Za-z0-9@=.,_+-]
+with
+.B %nn
+where nn is the two digit hex encoding. The message ID is a valid Xapian
+query, quoted using Xapian boolean term quoting rules: if the ID contains
+whitespace or a close paren or starts with a double quote, it must be
+enclosed in double quotes and double quotes inside the ID must be doubled.
+The astute reader will notice this is a special case of the batch input
+format for \fBnotmuch-tag\fR(1); note that the single message-id query is
+mandatory for \fBnotmuch-restore\fR(1).
+
+.RE
+.RE
+