Watchguard Firebox X1000 Reference Manual page 108

CHAPTER 7: Out-of-Band Initialization Strings
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\t
Send or expect a tab character
\\
Send or expect a backslash character
\ddd
Collapse the octal digits (ddd) into a single ASCII character and
send that character. Some characters are not valid in Ctrl+C; for
these characters, substitute the sequence with the control
character represented by C. For example, the character DC1 (17) is
shown as Ctrl+Q. Some characters are not valid in expect.
WatchGuard Firebox System