Hook the support already existing for evaluating up to a given line in the source file.
Considering that now worksheet's evaluation is trigerred after saving the document (#3), and the user can interrupts evaluation at any point in time by just start typing in the editor (#36), I think that rebuilding up to a line is now far less needed that initially supposed.
rebuilding up to a line
I'm moving this ticket to the next milestone.
And #52 would be a much nicer alternative. AFAIC, I'd close this ticket (but I'm leaving it open to see what Iuli thinks of it).