Changes

The <code>\arrangedpageA</code> and <code>\arrangedpageB</code> are box registers that you can use to build up your desired output pages. They actually go up to <code>\arrangedpageH</code>. If  ''Note:'' if your imposition scheme needs more than eight physical pages see below [[#Imposition_by_signatures|Imposition by signatures]] on how to interface with an external imposer program.

https://source.contextgarden.net/tex/context/base/mkiv/page-imp.mkiv?search=poparrangedpages.+

there are various versions alternative definitions of <code>\poparrangedpagesAB</code> that use manipulate to box registers in different ways to output the desired imposition. The macro <code>\installpagearrangement</code> makes the generic <code>\poparrangedpages</code> use one of those alternatives (in this case <code>\poparrangedpagesAB</code>).