[bug #59823] [ms] re-implement PN register

[G. Branden Robinson]

Follow-up Comment #1, bug #59823 (project groff):

On further thought this might be really easy.  I may have already done the
"hard" part in the quoted commit.  The _only_ time the page number is parsed
is in the PT macro, which is now defined as follows.


.de PT
.\" To compare the page number to 1, we need it in decimal.
.ds pg*saved-page-number-format \\g%\"
.af % 0
.nr pg*page-number-in-decimal \\n%
.af % \\*[pg*saved-page-number-format]
.ie \\n[pg*page-number-in-decimal]=1 .if \\n[pg*P1] .tl \\*[pg*OH]
.el \{\
.       ie o .tl \\*[pg*OH]
.       el .tl \\*[pg*EH]
.\}
..


Access to % is serialized because the formatter is single-threaded (in
general, but more importantly with respect to input processing), so our
meddling with its format is invisible to any other operation that might access
%...including access through an alias.

So I am now thinking that this bug can indeed be resolved by throwing


.aln PN %


over the wall at an appropriate point in initialization and have done with it.
 Even if the user assigns a format to % or PN, they will never be able to
observe it while we have it temporarily set to decimal inside PT.

Lesk encourages the user to redefine PT if desired, so this point may be worth
noting in the documentation update portion of this bug's resolution.

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