> I think that the vertical position is initialized to -1 before any
> text has been output is also by design, to be able to set page
> margins on the first page with a ".wh 0 xx" trap. To quote the
> Troff User's Manual:
>
> A pseudo-page transition onto the first page occurs either when
> the first break occurs or when the first nondiverted text
> processing occurs. Arrangements for a trap to occur at the top of
> the first page must be completed before this transition.
Or to quote the info manual of groff:
-- Register: \n[nl]
This register contains the current vertical position. If the
vertical position is zero and the top of page transition hasn't
happened yet, `nl' is set to negative value. `gtroff' itself does
this at the very beginning of a document before anything has been
printed, but the main usage is to plant a header trap on a page if
this page has already started.
Consider the following:
.de xxx
. sp
. tl ''Header''
. sp
..
.
First page.
.bp
.wh 0 xxx
.nr nl (-1)
Second page.
Result:
First page.
...
Header
Second page.
...
Without resetting `nl' to a negative value, the just planted trap
would be active beginning with the _next_ page, not the current
one.
Werner
