We used to have a two-step process for answering questions. On the first page the user indicated how he would answer: either by typing a response or uploading a file. On the next page either a textarea or file input was presented. Instead I plan to present a single page where the user can do either of those things, but not both. What is the most user-friendly way to do this?
You could create 2 radiobuttons. So that the user can make the choice whether he wants to add text or upload a file.
Or you could even do it without the radiobuttons and let the user click on the element he wishes to use.
If you do this it is very important to also check it at the backend code (php / asp / whatever) since it would be trivial to circumvent this (by disabling JS or by changing the DOM).