logging: clarified documentation for Handler.handleError.

Doc/library/logging.rst

@@ -375,12 +375,14 @@ subclasses. However, the :meth:`__init__` method in subclasses needs to call
 .. method:: Handler.handleError(record)
 
    This method should be called from handlers when an exception is encountered
-   during an :meth:`emit` call. By default it does nothing, which means that
-   exceptions get silently ignored. This is what is mostly wanted for a logging
-   system - most users will not care about errors in the logging system, they are
-   more interested in application errors. You could, however, replace this with a
-   custom handler if you wish. The specified record is the one which was being
-   processed when the exception occurred.
+   during an :meth:`emit` call. If the module-level attribute
+   ``raiseExceptions`` is ``False``, exceptions get silently ignored. This is
+   what is mostly wanted for a logging system - most users will not care about
+   errors in the logging system, they are more interested in application
+   errors. You could, however, replace this with a custom handler if you wish.
+   The specified record is the one which was being processed when the exception
+   occurred. (The default value of ``raiseExceptions`` is ``True``, as that is
+   more useful during development).
 
 
 .. method:: Handler.format(record)