grafana/grafana — pull request #1210 by falkenbt (2014-12-09 16:24:36+00:00)
Title: Extend tooltip for drilldown link

It took me a bit to find out that variables need to be passed with var-variableName.
The behavior is not specific to the drilldown link but I couldn't find it in any documentation elsewhere and it might help others to have it documented right here.