For example, "ledger eval options.limit" prints 0 (for false), but:
"ledger -l hello eval options.limit" print "hello"s, since the value of
options.limit, once set to a value, is that string. For flag options,
such as -Y, eval prints 0 if unset, and 1 if set.
This feature allows value expressions to be conditionalized based on the
presence of user options.
-- to mean special things after the command verb was seen. But now, what used
to be specified as this:
ledger -n reg cash -payable -- shell
Is now specified as this:
ledger reg -n cash not payable @shell
It could also be specified as:
ledger -n reg \(cash and not payable\) and @shell
