title: How can I "remind" users to fill in cells on a worksheet
body: <p>Hello:  I have a set of cells on a worksheet called "Docs".  The cell range is (B13:C23).
  When users get taken to this page, they are meant to fill out each of these cells with a value from 0 through 6. My Question:  Is there some code that I can attach to this sheet where, if a user does not fill in a cell with anything (ie. leaves it blank) and tries to leave the sheet or close the workbook, they are somehow reminded to fill it in?  Or is there a way to not let them leave the sheet until it's completed?  Thanks.. Allan</p>