When changing text in multiple columns, it should be possible to specify that
the change bar appears in the gutter of the column containing the text or all
the way over in the page margin regardless of which column contains the changed
text.  When appearing in gutters, change bars should also be constrained to the
gutter area and not overlap text in an adjacent column.

You should also have the option of placing change bars inside a table cell.

Also, prevent line numbers and change bars from overlapping when both are
present on the same line and side of the page.  Provide a way for change bars to
be either left, right, inside, or outside of the line numbers.

Could also position change bars relative to the printable boundaries of the page
rather than the page margin.