lix/doc/manual/rl-next/short-expr-flag.md

synopsis
reintroduce shortened `-E` form for `--expr` to new CLI

In the past, it was possible to supply a shorter -E flag instead of fully specifying --expr every time you wished to provide an expression that would be evaluated to produce the given command's input. This was retained for the --file flag when the new CLI utilities were written with -f, but -E was dropped.

We now restore the -E short form for better UX. This is most useful for nix eval but most any command that takes an Installable argument should benefit from it as well.