Omegalight27 The release notes for the "On Hit Script" feature contains all of the specifics in regards to what can be referenced within the script (in this case, special variables that are available, like $target):
Added "On Hit Script" option for weapon items ($weapon will contain the weapon item's codex, $target the hit entity, $damage the damage amount, and $projectile the projectile entity)
Below is the link to the full changelog history going back to v0.5, which is a great source of information on new features and functionality that are added. As it's usually not feasible to keep the official docs completely up to date, I always try to include any necessary details in the release notes until I can get the docs filled in.
RPG in a Box changelogs:
https://docs.google.com/document/d/1rLBEc6BXul6tRWVvmR06Ongkn0vswucPwqt5yL7aov8