Syntax for legend options {{hostname}}?

What is the syntax for Legend options. Specifically where I currently have {{hostname}} {{ifName}} I would like it to show hostname and (ifAlias or ifDescr or ifName) in that order.

Something like {{hostname}} {{ifAlias|ifDescr|ifName}} with preference on the left.

If no other options are available other than label value substitution, how could I accomplish this? Not all of my interfaces have descriptions of aliases defined, but if they are defined I prefer to see those instead of the interface name.