Create Datum Plane make two of them

[Vagulus]

I have created a Datum Plane offset from the Global XY Plane and I get offered these options.

220119 Datum Plane Selections 640x448.png (57.95 KiB) Viewed 484 times

These are not mentioned in [wiki]https://wiki.freecadweb.org/PartDesign_Plane[/wiki].

Would someone please explain what these options do?

When I accept the default option I discover that I have two Datum Planes in the Tree.

220119 Two Datum Planes.png (14.18 KiB) Viewed 484 times

(1) Why are there two?
(2) Which one do I use to build another body on?
(3) Just by way of tidying up, how do I get rid of the one I do not use?

OS: Windows 10 Version 2009
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.24291 (Git)
Build type: Release
Branch: releases/FreeCAD-0-19
Hash: 7b5e18a0759de778b74d3a5c17eba9cb815035ac
Python version: 3.8.6+
Qt version: 5.15.2
Coin version: 4.0.1
OCC version: 7.5.0
Locale: English/New Zealand (en_NZ)

[TheMarkster]

If you create a new datum plane with the xy plane selected, then the datum plane gets attached to that plane. The datum plane goes into the currently active body. If you select the xy plane of another body, then how does FreeCAD handle this? The datum plane cannot reference the xy plane of another body without a shapebinder, so one gets created for you. Now you have a datum plane and a shapebinder in the new body. What you should do instead is select the plane in the active body and create a datum plane instead of a plane from a different body.

[Vagulus]

Great! Thanks.

BTW: it would be nice if one of the Druids updated the Wiki to deal with these things.
I appreciate that you all have other priorities - but it would be nice.