$options['specIsArg'] is documented as
If set and truthy, default $spec['spec_is_arg'] = true if it is unset. This is mainly intended for backwards compatibility with existing code that uses a near-clone of ObjectFactory with those semantics.
However, this is only used in a single place, the construction of FileJournal objects. I suggest deprecating this functionality
Codesearch: https://codesearch.wmcloud.org/search/?q=specIsArg&i=nope&files=&repos=