Facebook for Developers has a “Was this document?” button stuck at the button-right of the page. You can select “Yes”, “Yes, but…”, and “No.”
When you select “Yes” a confirmation appears to thank you for your feedback:
When you select “Yes, but…”, a modal appears with several checkbox categories and a text area to send comments:
When you select “No”, the same modal as the “Yes, but…” response appears but with slightly different leading text:
If you close the feedback feature, a “Give Feedback” button appears.