A few questions on registers, and on processors used with registers:

Can processors be used on entries in \setregisterentry? My tests so far have not been successful.

Can processors be used on one level of a two-level register {\index{Name+Processor->quotation precis}? Again, no success with attempts.

Can something other than page numbers be the indexed item?

I have a book with many quotations, each identified by a number (generated by \definelabel). For an index of quotations, it would be more useful to point to that quotation number than the page number.

Perhaps the last requirement would be served by building a list with the quote number and quotation precis, suppressing the page numbers with pagenumber=\gobbleoneargument. But placelist does not seem to behave as one would hope. The example in the wiki for setuplist (shown below) does not print the numbers (1., 2.) in the first braced argument to writetolist.
\definelist[Reprints][criterium=all]

\starttext
  \section{Sec 1}
  \writetolist[Reprints]{1.}{List entry A}
  \subsection{Subsec 1}
  \writebetweenlist[Reprints]{\hrule}
  \writetolist[Reprints]{2.}{List entry B}
  \completelist[Reprints]
\stoptext
I would prefer a register solution to take advantage of similar formatting (column support and such) provided there, since this will appear with the book’s standard indices.

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Rik