The purpose of this website

These pages describe how something works. They are not a substitute for advice that takes a reader's own position into account.

Other websites

External pages change without notice. What a link pointed to when it was added may not be what it points to today.

Accuracy of the information

If a detail here would change what someone does, confirm it at source before acting on it. Nothing here is warranted as fit for that purpose.

Keeping this current

Any change is made on this page rather than notified separately. The version in force is the one shown above.

Reporting an error

For anything to do with the material published here, write to [email protected].