How to use kak_selection?

Thanks a lot.
You help me to think well.
I solved the issue with :

map global user -docstring 'open FZF fuzzy word finder' g ':@ rfzf %sh{ echo "$kak_selection" };tmux-terminal-zoom 1<ret>'

For information, if someone need it, the rfzf script is as :

#!/usr/bin/env bash
RG_PREFIX="rg --column --line-number --no-heading --color=always --smart-case "
INITIAL_QUERY="${*:-}"
: | fzf --ansi --disabled --query "$INITIAL_QUERY" \
    --bind "start:reload:$RG_PREFIX {q}" \
    --bind "change:reload:sleep 0.1; $RG_PREFIX {q} || true" \
    --delimiter : \
    --preview 'bat --color=always {1} --highlight-line {2}' \
    --preview-window 'up,60%,border-bottom,+{2}+3/3,~3' \
    --bind 'enter:become($EDITOR {1} +{2})'

And I use the plugin connect.kak for the command :@ rfzf :
kakounedotcom/connect.kak: Connect a program to Kakoune clients (github.com)