Where is the tutorial by, I think, Charles, that shows Andy lying on a "bed" and draping a plane over him like a sheet?

I watched it once and should have noted where it is because I need to watch again.

tutorials in general: where are the best Poser tutorials?

drawn

https://www.renderosity.com/premium-tutorials/11/lesson-05-cloth-room

You will find all the Poser tutorials under Community > Tutorials > Poser on the title banner.

yes, I went there before I posted this question but that particular tune isn't there? somewhere else...

drawn

https://www.posersoftware.com/poser-tutorials

Also has tutorials. As to where that one is--I have no idea, sorry.

That tutprial is on page 7 or the Poser premium tutorials. There are several tutorials there for dynamic clothing.