Watchguard Firebox X20E Reference Manual page 58

Modem initialization strings
\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.
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