The following is an example of using the HTML5 output tag with both an onforminput event added to it as well as a oninput tag added to it's form. Back to the User Agent Man oninput article.
output
onforminput
oninput
Enter in a value below. The output field will tell you which event(s) were fired as a result. It is best not to have both onforminput and oninput events on the same page (the former is deprecated anyways).