gbranden pushed a commit to branch master
in repository groff.
commit 3bd200886c9c2a0212d6cb9db48a8d09f606b12f
Author: G. Branden Robinson <[email protected]>
AuthorDate: Mon Dec 1 18:33:39 2025 -0600
doc/groff.texi.in: Expand discussion of `nl` reg.
---
doc/groff.texi.in | 31 ++++++++++++++++++++++++++-----
1 file changed, 26 insertions(+), 5 deletions(-)
diff --git a/doc/groff.texi.in b/doc/groff.texi.in
index 290b1ab39..7cb4d65e3 100644
--- a/doc/groff.texi.in
+++ b/doc/groff.texi.in
@@ -11245,11 +11245,32 @@ Spacing}). While the @code{sv} request allows
negative values for
@cindex drawing position, vertical (@code{nl})
@c TODO: We should talk somewhere prior to this point about how the
@c formatter doesn't start a page until it has to.
-@code{nl} interpolates or sets the vertical drawing position. When the
-formatter starts, the first page transition hasn't happened yet, and
-@code{nl} is negative. If a header trap has been planted on the page
-(typically at vertical position @code{0}), you can assign a negative
-value to @code{nl} to spring it if that page has already started
+@code{nl}
+interpolates the vertical drawing position
+as of the most recently typeset output line.
+It does not necessarily
+(and often does not)
+represent that of the pending output line,
+because the formatter does not determine the position of its baseline
+until it is output;
+recall @ref{Manipulating Spacing}.
+Assigning a value to
+@code{nl}
+sets the vertical drawing position
+in advance of further modifications to baseline positioning
+arising from alterations to type size,
+changes to vertical spacing,
+or application of extra pre- or post-vertical spacing.
+
+When the formatter starts,
+the transition to the first page has not yet happened---@code{nl}
+is negative.
+If you plant a page location trap at vertical position
+@samp{0}
+(idiomatically to format a header),
+you can assign a negative value to
+@code{nl}
+to spring that trap even if the page has already started
(@pxref{Page Location Traps}).
@Example
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