be very flexible in the way time shifts are specified and applied...</p>

<p>The ability to shift dates by Y years, M months, etc, conflicts with the design goal of maintaining a constant shift for all time values when applying a batch shift. This is because shifting by 1 month can be equivalent to anything from 28 to 31 days, and 1 year can be 365 or 366 days, depending on the starting date.</p>

<p>The inconsistency is handled by shifting the first tag found with the actual specified shift, then calculati