Michał Kępień authored Feb 06, 2019 and Evan Hunt committed Feb 06, 2019

Add a warning about potential performance implications of configuring a
non-root zone as a mirror zone.  Explain in more detail how each mirror
zone version is validated and how validation failures are handled.  Move
the paragraphs describing how to set up IANA root zone mirroring higher
up, so that they can be more easily found by the reader.  Explicitly
state that the "masters" option needs to be present for any mirror zone
which is not the root zone.  Tweak the description of the interaction
between the "dnssec-validation" setting and root zone mirroring to make
it less ambiguous.  Specify what the default "notify" setting is for
mirror zones.