[Zope] zope.conf read-only settings

AFAICS the directives zserver-read-only-mode and read-only-database just set the environment value ZOPE_READ_ONLY and no change in ZOPE's operation results. Am I right? This is ZOPE 2.7.7 Setting read-only in the database storage does make a difference (in my configuration, Formulator 1.6.2 throws an exception, but that's not a ZOPE issue). Steven