Here is the man page source code of /usr/share/man/man1/docker-attach.1.gz:
#+BEGIN_EXAMPLE
.PP
To override the sequence for an individual container, use the
\fB\fC\-\-detach\-keys="<sequence>"\fR flag with the \fB\fCdocker attach\fR command. The format of
the \fB\fC<sequence>\fR is either a letter [a\-Z], or the \fB\fCctrl\-\fR combined with any of
the following:
.IP \(bu 2
\fB\fCa\-z\fR (a single lowercase alpha character )
.IP \(bu 2
\fB\fC@\fR (ampersand)
.IP \(bu 2
\fB\fC[\fR (left bracket)
.IP \(bu 2
\fB\fC\\\\\fR (two backward slashes)
.IP \(bu 2
\fB\fC\_\fR (underscore)
.IP \(bu 2
\fB\fC^\fR (caret)
#+END_EXAMPLE
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