* Ensure the version file is closed after reading its content.
1.2.7
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* Changed how illegal XML characters are sanitized, to speed the operation. The old way was removing more characters than are required by the XML specification.
1.2.6
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* Add support for relative dates to DateTime fields.
1.2.5
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* Changes for Python 2/3 compatibility.
1.2.4
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* Added an API for notifying the Runtime when an XBlock's ``save()`` method is called.
* Added a mechanism for Runtime subclasses to more easily add extra CSS classes to the ``<div>`` that wraps rendered XBlocks
1.2.3
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Allow Mixologist class to consume both class objects and string paths to classes as a part of initialization.