Spreadsheet 2000 / Product Requirements Document

Spreadsheet 2.0 is getting good reviews, but we want just a couple of minor things...

Feature: Persistence

Some people are using spreadsheets to calculate networks of complicated formulas.  They're getting tired of typing them in all the time.  They would like to be able to save and load spreadsheets from disk files.

Add save and load functions to the Spreadsheet class.  They should save the spreadsheet data to a file, and load it from a file.

Feature: Undo

Users would like to be able to undo their changes.  They should be able to undo at least the last change to any cell.  The undo should not only restore that cell's original value, but the values of any cells that were automatically updated by updating that source cell.