Creating a "footer part" that overlaps the "body part"
The body part will still scroll but will have a limited window. In web design, we call these frames or panes.
This is for extended help text to enable he user to get contextual help as they are completing a question. As I have say about 160 fields aligned vertically I can't have the footer part right at the bottom as it would mean the user has to scroll right to the bottom, defeating the purpose of help text right there and then.