+* New methods were added to ApiBase to handle errors and warnings using i18n
+ keys. Methods for using hard-coded English messages were deprecated:
+ * ApiBase::dieUsage() was deprecated
+ * ApiBase::dieUsageMsg() was deprecated
+ * ApiBase::dieUsageMsgOrDebug() was deprecated
+ * ApiBase::getErrorFromStatus() was deprecated
+ * ApiBase::parseMsg() was deprecated
+ * ApiBase::setWarning() was deprecated
+* ApiBase::$messageMap is no longer public. Code attempting to access it will
+ result in a PHP fatal error.
+* The $message parameter to the ApiCheckCanExecute hook should be set to an
+ ApiMessage. This is compatible with MediaWiki 1.27 and later. Returning a
+ code for ApiBase::parseMsg() will no longer work.
+* UsageException is deprecated in favor of ApiUsageException. For the time
+ being ApiUsageException is a subclass of UsageException to allow things that
+ catch only UsageException to still function properly.
+* If, for some strange reason, code was using an ApiErrorFormatter instead of
+ ApiErrorFormatter_BackCompat, note that the result format has changed and
+ various methods now take a module path rather than a module name.
+* ApiMessageTrait::getApiCode() now strips 'apierror-' and 'apiwarn-' prefixes
+ from the message key, and maps some message keys for backwards compatibility.