[pdftex] \pdfsavepos and friends

[Marco Loskamp]

Dear list,

I've recently begun playing around with some of the new primitives that
haven't been documented in  the  versions of the  PDFTeX documentation.
The syntax-file  (www.tug.org/applications/pdftex/pdftex-syntax.txt) is
quite helpful in that respect, except that for some reason I can't make
commands using "(h, v, m)" run; <---,
                                     \
I'm specifically interested in drawing|arrows from within the text to a
math display, something like "and here|, you can see that I really need
some extra help".   (This all in *plain* pdfTeX,  i.e. only   plain.tex
loaded internally.)
If this is doable with (a subset of) the following commands, I'd deeply
appreciate if you could give me some specific advice.

  \pdfsavepos                      (h, v, m)
  \pdflastxpos                     (read-only integer)
  \pdflastypos                     (read-only integer)
  \pdfsnaprefpoint                 (h, v, m)
  \pdfsnapx <glue spec>            (h, v, m)
  \pdfsnapy <glue spec>            (h, v, m)
  \pdflinesnapx <glue spec>        (h, v, m)
  \pdflinesnapy <glue spec>        (h, v, m)


Thanks in advance!
Marco

PS
Here's what I have found by searching for "pdfsavepos" under google.com
(excluded links for MacOS, those in Czech, the pdftex.pool or
pdftex-syntax.txt files, and conTeXt-related):

http://www.ntg.nl/maps/pdf/25_10.pdf

  (maybe that's the one I need, but I couldn't quite extract the pdftex-
  specifics from the EMTeX examples. Please refer me back if you think
  that this solves my question already!)

http://www.tug.org/pipermail/pdftex/2003-April/003873.html

  This thread seems a little off-topic (with respect to pdftex at its
  primitive level), and doesn't explicitely mention how to use those
  commands.