I think you can provide a precise specification without losing simplicity of explanation. Maybe something like
When step is positive, zero rows are returned if start > stop. Conversely, when step is negative, zero rows are returned if start < stop. It is an error for step to be zero.
Having something that generates a list of dates would be handy, however I guess you can do it with the current series generator by adding that many day intervals to a base date...
Chris
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