ifOutDiscards(_rate) can not be alerted

According to the documentation if you create an alert on ifOutErrors_rate, you wil also get the discards:
http://www.observium.org/docs/alerting_examples/

However it looks like that is not the case. Also we would like to have to option to create an alert on ifOutDiscards_rate if it's gt 1.
Now it is not possible to have any alerting if you have output or input drops on any interface. This is very important if you do any QOS or have any other issues in overloading queues.
Only interface errors (CRC and other ) can be alerted.