Hi,
please excuse this problem. It seems to be a result from this process:
Note we are making changes to the documentation site
So please bear with us whilst this is in progress.
The working solution is to combine the v3.9 and v4 documentation and ensure article titles have either V3.9 or V4 or both at the end of the title.
Presently some links to other articles are not working - this is being resolved
I will contact Colin who is currently making these changes. He will put the required information back online.