Finally got it in a pot. This is clematis ligusticifolia, 'Western White Clematis', blooms in midsummer. Its a perrenial, so am I right to assume I can treat it like any other perrenial and whack off any bits that get out of bounds? That would be any attempt to overgrow my neighbor's shed. Mobile home lots are small and close, donchano. Now to figure out exactly WHEN midsummer might be around here, I guess it will be whenever the clematis blooms. Reading this forum is making me want more of them.

Try not to whack off pieces but encourage them to grow on your form by twirling them around the metal pieces. They are the pieces that will provide blooms.

This article states it can get to 15' so you just might want to scout out a place where it can roam freely.
https://www.anniesannuals.com/...

This article states 20' for your 'Western White' clematis!

My "plan" is to twine it around those top pieces and then start it back down, like a curtain. I've also thought about using some of those Shepherd's Hooks to drape it around the general area.

Have fun training it. At 15 to 20' it will keep you busy!

Do they only bloom from the end of the stem? Or can they bloom from other places? Would early pinching help, or am I living in a fantasy world?

I wouldn't pinch!

My photo program isn't cooperating right now but I'll try again in the morning.

These photos should help with your questions:
Mountain Clematis (Clematis montana)

Ok, I kinda get it. This thing will do its own thing and I'll adjust my thinking when I find out what its "thing" is. I can wait. There are lots of other plants to play with while I wait for midsummer. Thanks for the info.

It can go wild so have fun watching it and don't fear transplanting it if it gets too wild.

This is like having kids. I told them several times that if I wanted teenagers I would have had them in the first place. All I wanted was the little baby. Now I've got a potential monster in the garden because I wanted those pretty flowers. There's no problem moving it since its in a pot. This WILL be fun.

Great attitude!