The command line parser is based on libtecla, a freely available library. If the file $HOME/.teclarc exists, then libtecla will use it to configure the key bindings.
By default, libtecla uses emacs key bindings. There is no need for any further libtecla configuration if emacs mode is desired.
In order to use the vi editor key bindings, the $HOME/.teclarc file must exist, and it must contain the following line: edit-mode vi
Custom key bindings are also available. Refer to the libtecla documentation for more details on command line editing key customization.