Scripting: Available Properties on item parameter

Can someone provide a model of the available properties on the item parameter that gets passed into the script. I know I can type 'item.' and get a list of the properties, but I was wondering if this is documented anywhere since I don't see it in the UserGuide.

I'm also wondering what JS engine is being used to run the scripts and what version of JS is supported, I noticed some things I have tried in the past didn't work. Unfortunately it has been a while so I can't remember specifics on what didn't work.

Is there something I can do in the script to get the NewFileName column to be blank for files that don't meet certain criteria without an error, so I can easily see the files that will/won't get changed? I have tried just 'return;', 'return null;', and not returning anything.