I mean... Let's that we just make an AJAX request and inser the result inside a div#result..
In the backend the script use ob_flush() to send the header but not terminate the request until it's terminated (with exit or ob_flush_end)
The content will be loaded into the #result only when the request terminate (exit or ob_flush_end) or it'll be loaded every time the script send the header by ob_flush?
Update:
I'll use jQuery load() to make the request & PHP to answer it