Hi Keith
Some of the variables that we made available to users (not including any field expression) can be found in the online help documentation. I used to be able to search by “CurrentUserID” for example to locate the part of the help file but I seemed unable to do it now. We will look into this. But for the list of variables you are looking for, we have a couple of places mentioning them (probably a good idea to consolidate them in one list and one page). As mentioned, you can search for “FilePath” and find the use of this variable.
Some other variables, such as CurrentUserName, CurrentUserID, and CurrentUserEmail can be found to be used in System Integration Web Part as Input, such as the screen shot of the help page included below – I will also need to check with the documentation team as I cannot locate them in the new help files today.