Added documentation in update document for new error handling

docs/upgrading.rst

@@ -91,6 +91,33 @@ handling::
 
     # and here it's gone
 
+Manual Error Handler Attaching
+``````````````````````````````
+
+While it is still possible to attach error handlers to
+:attr:`Flask.error_handlers` it's discouraged to do so and in fact
+deprecated.  In generaly we no longer recommend custom error handler
+attaching via assignments to the underlying dictionary due to the more
+complex internal handling to support arbitrary exception classes and
+blueprints.  See :meth:`Flask.errorhandler` for more information.
+
+The proper upgrade is to change this::
+
+    app.error_handlers[403] = handle_error
+
+Into this::
+
+    app.register_error_handler(403, handle_error)
+
+Alternatively you should just attach the function with a decorator::
+
+    @app.errorhandler(403)
+    def handle_error(e):
+        ...
+
+(Note that :meth:`register_error_handler` is new in Flask 0.7)
+
+
 Version 0.6
 -----------
 

flask/app.py

@@ -822,6 +822,15 @@ class Flask(_PackageBoundObject):
             return f
         return decorator
 
+    def register_error_handler(self, code_or_exception, f):
+        """Alternative error attach function to the :meth:`errorhandler`
+        decorator that is more straightforward to use for non decorator
+        usage.
+
+        .. versionadded:: 0.7
+        """
+        self._register_error_handler(None, code_or_exception, f)
+
     def _register_error_handler(self, key, code_or_exception, f):
         if isinstance(code_or_exception, HTTPException):
             code_or_exception = code_or_exception.code