Viper Is a Package for Emacs Rebels: Unimplemented Features

Unimplemented features include:

:ab and :una are not implemented, since :ab is considered obsolete, since Emacs has much more powerful facilities for defining abbreviations.
:set option? is not implemented. The current :set can also be used to set Emacs variables.
:se list requires modification of the display code for Emacs, so it is not implemented. A useful alternative is cat -t -e file. Unfortunately, it cannot be used directly inside Emacs, since Emacs will obdurately change ‘^I’ back to normal tabs.