Why are join/connected methods virtual?

[matthijskooijman]

Reading the code, I see that various join methods, and the connected method are declared virtual. Why is this? Are subclasses expected that only subclass these methods? Or is this just a typo / accidental copy-paste?

There are also some other methods overridden from the Stream class that are already virtual there, so those make sense to be virtual.

[HeadBoffin]

It would appear to be a muddle, hacked out of a GPS library - certainly not nice clean clear code for alterations.