The Underline flag (&) causes the next character to be
    underlined.

    The operation performed by this flag (as opposed to the flag's
    recognition) can be disabled and reenabled by the .DISABLE
    UNDERLINING and .ENABLE UNDERLINING commands.

    The Underline flag can be paired as follows:

    o  With the Uppercase flag (^&) to turn underlining on and with
       the Lowercase flag (\&) to turn underlining off.

    o  With the Space flag (&#) to cause the underlining of
       unexpandable spaces.