Terminal multiplexers like (screen, tmux, ...) do not support the kitty
image protocol (as of yet), to go around this DCS escape sequences are
used (`\ePtmux;...\e\` for tmux, `\eP...\e\` for screen). This option
allows passing thorugh the kitty image escape sequences.
`\033\\` suffixes from `KITTY_ESC_IMG_SHM` and `KITTY_ESC_DELETE_ALL`
have been removed. This makes it easier to wrap the escape sequences in
a DCS control sequence since there will be no `\033` in them to escape
(as multiplexers require escaping the escapes within the DCS data
string). `DCS_GUARD_WRITE` and `DCS_GUARD_APPEND` macros have been added
to wrap escape sequences in DCS control sequence based on the
availability of the `priv->dcs_prefix` property.
한승민
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