Assigned to Denis for Hayes+.
Our editing experience is not ideal for larger documents, because the editor is constrained to a fixed height, which is inside a page which has a variable width. What happens is we end up with two sets of scrollbars which can become incredibly annoying when editing long documents. The goal of this viewport feature is to expand the editor's height dynamically to match the height of the inner contents. We should never have a scrollbar when editing.
This is a proof-of-concept prototype done for just a simple TEXTAREA: http://roykim.net/sandbox/textarea
Note: This prototype doesn't handle the "adding new lines" case very well. This code shouldn't be used - it's just a proof of concept.