Support setting the xterm clipboard when copying from copy mode using

the xterm escape sequence for the purpose (if xterm is configured to
allow it).

Written by and much discussed Ailin Nemui, guidance on
xterm/termcap/terminfo from Thomas Dickey.

tmux.1

@@ -1705,6 +1705,28 @@ Available server options are:
 Set the number of buffers; as new buffers are added to the top of the stack,
 old ones are removed from the bottom if necessary to maintain this maximum
 length.
+.It Xo Ic set-clipboard
+.Op Ic on | off
+.Xc
+Attempt to set the terminal clipboard content using the
+\ee]52;...\e007
+.Xr xterm 1
+escape sequences.
+This option is on by default if there is an
+.Em \&Ms
+entry in the
+.Xr terminfo 5
+description for the client terminal.
+Note that this feature needs to be enabled in
+.Xr xterm 1
+by setting the resource:
+.Bd -literal -offset indent
+disallowedWindowOps: 20,21,SetXprop
+.Ed
+.Pp
+Or changing this property from the
+.Xr xterm 1
+interactive menu when required.
 .It Ic escape-time Ar time
 Set the time in milliseconds for which
 .Nm
@@ -2796,6 +2818,21 @@ If the command doesn't return success, the exit status is also displayed.
 .D1 (alias: Ic info )
 Show server information and terminal details.
 .El
+.Sh TERMINFO EXTENSIONS
+.Nm
+understands some extensions to
+.Xr terminfo 5 :
+.Bl -tag -width Ds
+.It Em \&Ms
+This sequence can be used by
+.Nm
+to store the current buffer in the host terminal's selection (clipboard).
+See the
+.Em set-clipboard
+option above and the
+.Xr xterm 1
+man page.
+.El
 .Sh FILES
 .Bl -tag -width "/etc/tmux.confXXX" -compact
 .It Pa ~/.tmux.conf