Test detailed with line breaks in message - optionStringMultiline?

I'd like to put line breaks in some long error messages of a test using detailed-0.9. There is an option that is named like it could/should be doing this, but setting optionStringMultiline does not have any effect.

Since this there is no documentation and optionStringMultiline shows up in the cabal source only there and does not seem to be used: is it implemented at all? Where would this option be used?

I tried:
a) adding this in options:
TestInstance {
run = return (Finished r)
, name = name
, tags = []
, options = [OptionDescr "ml" "multiline" (OptionString True) Nothing]
, setOption = \_ _ -> Right

b) wrapping the test in ExtraOptions:
ExtraOptions [OptionDescr "ml" "multiline" (OptionString True) Nothing] $
...