Which FET versions work
What we test against, what happens to a file from an older or a newer FET, and the promise that matters more than a version number.
What we test against
FET 7.11.1. Every release is checked against real FET files, and the strictest test we run asks FET itself for a verdict: a file FET can solve must produce no errors here.
Older files
They open. FET files have been the same shape for a long time, and a file written by an older FET is read the same way.
We do not upgrade them. When you download your timetable, it carries the version your own file declared. We do not stamp a newer number on it and we do not rewrite it to a newer shape. It goes back to the FET you use.
Newer files, and files from a fork
Some schools use a fork of FET, or a version newer than ours. Those files carry rules this product has never heard of.
⛔ A rule we do not recognise survives. It is written back unchanged, in place. We do not drop it, and we do not guess at it.
⚠ What we will not do is check a rule we do not understand. It is carried, not interpreted. The check is silent about it rather than guessing, and silence here means "not examined", never "fine".
The promise that matters more than a version
Nothing you import is lost. That is the point of the two rules above: the version stays yours, and unknown rules travel intact.
A tool that quietly modernises your file, or quietly drops the parts it does not understand, costs you more than it saves — and you would find out at the worst moment, when FET refuses the file you got back.
If a file will not open
The check refuses a file rather than half-reading it, and it says why. The two common reasons are size and shape: a file above the size limit, or a file that is not FET XML at all.
⚠ A .fet file is XML. A CSV export from a spreadsheet is not a FET file, even when the timetable inside it is yours.