/usr/share/zsh/functions/Zle/move-line-in-buffer is in zsh-common 5.4.2-3ubuntu3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | #autoload
# Line motions that do not leave the current history entry,
# for editing in multi-line buffers.
# To use:
# autoload -Uz move-line-in-buffer
# zle -N up-line-in-buffer move-line-in-buffer
# zle -N down-line-in-buffer move-line-in-buffer
#
# then bindkey as you prefer
local hno=$HISTNO curs=$CURSOR
zle .${WIDGET:s/in-buffer/or-history} "$@" &&
(( HISTNO != hno && (HISTNO=hno, CURSOR=curs) ))
return 0
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