This part of the algorithm test the the general state of the file to be imported and determines if the import should even start. There is quite a bit more happening under the hood, but at its core this part of the algorithm is testing these two criteria.
- Has the file changed? If the file hasn't changed at all it won't be imported.
- Is there anything "abnormal" about the feed? This works as a safety net for when feeds come in with bad data.