Using "render" with the expression editor.

I am looking at one of Nifflas's files and he is using this line : Render X Position*24.
What does the render command generally do?

Is there some kind of list on the web that I can learn about all such unknown commands/functions that the expression editor can accept?

Are you sure its a command and not an variable (alterable value) named Render?

I think he most likely called a global value "Render X Position".

Ah yes indeed, it is a global value called "Render X Position". Thanks for clearing that up. A list of some commands/ keywords would still be helpfull though.

Everything in the expression editor is accessible via the 'retrieve data from object' menu