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**New Features**
- Added HTML validation. This will check that only fields which are allowed
to contain HTML have it, that the HTML is valid, and that only allowed tags
and attributes are included.
- Added indices in error and message paths. These indices make it easier to
figure out exactly which canvas is failing with an error (if indeed only a
few are failing).
- Added unique/non unique error aggregation. Using a ``unique_logging` property
on a ``IIIFValidator``, users can decide whether all errors and warnings will be
aggregated, or only unique ones. Here, unique means that only one instance of
each error/warning per resource will be saved (that is, if every canvas has error
A, then only the first instance of a canvas with error A will be saved).
- Added ``verbose`` property to ``IIIFValidatior``. When ``True``, every error and
warning will be logged immediatly to the screen when hit.
**Bugfixes**
- ``Annotations`` no longer log a warning when they are missing an ``id`` field.