No, this is no April Fool’s joke ;-)
With this instruction you can construct your very own Celtic knot, a pattern I used to find too complicated to design of my own.
The image shows a Celtic knot I created some time ago, but I still like it.
I have nearly forgotten about this technique, but now that I rediscovered it, I have several ideas how to use it more often.
Designing a Celtic Knot
The original site doesn’t exist any more and is now only available through webarchive: Designing a Celtic Knot (Constructing a Celtic Knot)