Getting descriptiveName in Email template common.ftl

In modifying <data dir>/config/_notifications/email/common.ftl

I would like to change the following line:

Change ${mod.displayVersion} ${pers} by ${mod.userName} ($modLink}):

to something like this:

Change ${mod.displayVersion} ${pers} by ${mod.user.descriptiveName} ($modLink}):

Where can I find a list of properties that I can use in the email templates?

Thanks