Shift-F7 = DefineDiff

        This function initializes diff.  It prompts for the window number
        and letter to diff, ignore leading space, ignore all space, ignore
        blank lines, ignore case, and ignore end of line.  Any two windows
        may be diffed.  Diff only requires that the windows be visible.

                               Diff prompts

      DIFF:  Enter first window number and letter (e.g. 1a) :
      DIFF:  Enter next window number and letter (e.g. 2a) :
      DIFF:  Start diff at (B)eginning of file or (C)urrent position? (b/c)
      DIFF:  Ignore leading spaces (y/n)?
      DIFF:  Ignore all space (y/n)?
      DIFF:  Ignore blank lines (y/n)?
      DIFF:  Ignore end of line (useful with reformatted paragraphs) (y/n)?


    F7 = RepeatDiff
        Once the diff has been defined, press RepeatDiff to find the next
        diff.