SSH, screen and XDISPLAY

# set future remote shells started by screen to have the correct XDISPLAY
% screen -X "setenv XDISPLAY $DISPLAY" #...

# set up the keystroke F1 to update the XDISPLAY in current shells
% screen -X "bindkey -k k1 stuff export XDISPLAY=$DISPLAY15" #...

# update the XDISPLAY in all current windows
% screen -X "at % stuff export XDISPLAY=$DISPLAY15" #...