/usr/share/zsh/5.5.1/functions
Edit: /usr/share/zsh/5.5.1/functions/edit-command-line (1184B)
# Edit the command line using your usual editor.
# Binding this to '!' in the vi command mode map,
# autoload -Uz edit-command-line
# zle -N edit-command-line
# bindkey -M vicmd '!' edit-command-line
# will give ksh-like behaviour for that key,
# except that it will handle multi-line buffers properly.
() {
exec