On 30/03/2015 13:11, Ulrike Fischer wrote:
> The expanding use of key-val syntax in class and package options
> means that packages can break due to unknown values. I just tumble
> over this example in a real document:
>
> \documentclass[index=totoc]{scrbook} \usepackage{acro}
> \begin{document} \end{document}
>
>
> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! ! LaTeX error:
> "kernel/boolean-values-only" ! ! Key 'index' accepts boolean values
> only.
>
>
> It is easy to provoke a similar error with e.g. siunitx:
>
> w \usepackage{siunitx} \begin{document} blub \end{document}
>
>
> I'm wondering what could/should be done to avoid such situations.
> Should package authors avoid package options altogether and use setup
> commands? Or can they (how?) parse the keys in the option list in a
> way which doesn't gives errors but imply ignores unknown values?
> Should the documentclass filter the options? How?
>
>
>

Ulrike, good question:-)

I know you know most of the answer below already but stating the obvious
seemed a good place to start:-)


The standard option processing processes options from both the
\usepackage and \documentclass commands, but in different modes
so that unknown keys only generate an error if used directly
on the package.

for KV options the problems seem to be

1) There's no support in the kernel (possibly we could do something
about that, but looked at it before but it's tricky, this code's a bit
delicate and used in every latex document. There is a big incentive not
to change it:-)

2) there are two levels corresponding to "unknown option"
the key not being known at all, or the value not being known
for this key when handled by the package.


(1) means there are several different package kv handlers around
(directly in the file, as in hyperref, or versions for xkeyval, or
kvoptions or l3keys ....


It seems that currently typically unkown keys are being ignored but
unknown values of "known" keys are generating an error.

Probably most compatible thing to do would be to process the
documentclass options in a mode that both unknown keys and values
were silently ignored, although there's an argument to say that
once you start getting richer syntax like this, packages should stop
handling the documentclass options, as weird effects will happen
if the keys just happen to have the same name or compatible values.

David













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