How to get head branch name

Following this the variable names like “DRONE_BRANCH” gives the base branch name but not the head branch name.
Why Need this: For some of the conditional checks, need head branch name as well. Tried REFSPEC but couldn’t find the value: drone-dashboard here
Plus is there any way to parse payload in drone.yml file itself like [“pull_request”][“head”][“ref”]

The head branch is stored in the DRONE_COMMIT_REFSPEC environment variable.