It looks like we have a consensus that we want certain defaults for the format which answers are expected in for code-golf. On that poll, the question arose twice, which input/output formats should be allowed for programs and functions.
So here is another poll. This one works different though. All the input/output methods are independent of each other, so there will be one answer per method. Upvote all you think are reasonable for the default. Downvote those which you think shouldn't be allowed unless the OP explicitly permits them.
To keep this remotely manageable, I have not posted individual answers for all possible inputs for functions. So there are only four: functions can take input/output via their arguments and return values. Or functions can use any method full programs can. I don't think there is any point in (say) allowing programs to take input from STDIN (only) and to allow functions to take input from ARGV (only) or something like that. If you disagree, please leave a comment.
If I've overlooked an I/O method, feel free to add your own answer.
Note: Some votes have been reverted because they were detected as serial voting. If you vote on multiple answers, please leave some time between votes.
A method is allowed if it has 5 net votes and at least twice as many upvotes as downvotes.
The current results of the polls are now part of the tag wiki. Please notify me, if results change significantly and the wiki should be amended.