I'm trying to set a random size for the paper with this command:
Paper.size = {random:small:medium:large}
msg(Paper.size)

But I get this error:
Error running script: Error compiling expression 'random:small:medium:large': SyntaxError: Unexpected character: :Line: 1, Column: 7

Is there a different format for doing this?

[duplicate post. Leaving a note here in case someone else sees it later and thinks this question hasn't received an answer. There's an answer in the other copy]