http response

Is it possible in php to get a hold of the response stream and see what has been sent already? I have a global php function, but it can't be called inside html <form> elements, because it creates its own form, and when you nest html forms things get weird. In this function, I want to check if there is already an open <form> tag in the response without a corresponding </form> tag. Is there any way to do this? Thanks!!