explain negative tcl (PR#18827)

git-svn-id: https://svn.r-project.org/R/trunk@87384 00db46b3-68df-0310-9c12-caf00c1e9a41

Author: maechler

src/library/graphics/man/par.Rd

@@ -1,6 +1,6 @@
 % File src/library/graphics/man/par.Rd
 % Part of the R package, https://www.R-project.org
-% Copyright 1995-2022 R Core Team
+% Copyright 1995-2024 R Core Team
 % Distributed under GPL 2 or later
 
 \name{par}
@@ -512,7 +512,8 @@ par(\dots, no.readonly = FALSE)
       relevant side, so if \code{tck = 1} grid lines are drawn.  The
       default setting (\code{tck = NA}) is to use \code{tcl = -0.5}.}
     \item{\code{tcl}}{The length of tick marks as a fraction of the
-      height of a line of text.  The default value is \code{-0.5};
+      height of a line of text.  Negative values give tick marks outside
+      the plotting region.  The default value is \code{-0.5};
       setting \code{tcl = NA} sets \code{tck = -0.01} which is S' default.}
     \item{\code{usr}}{A vector of the form \code{c(x1, x2, y1, y2)}
       giving the extremes of the user coordinates of the plotting
@@ -612,10 +613,10 @@ par(\dots, no.readonly = FALSE)
   short form (e.g, \code{"#rgb"} or \code{"#rgba"}). The short form is
   expanded to the long form by replicating digits (not by adding zeroes),
   e.g., \code{"#rgb"} becomes \code{"#rrggbb"}. Colors can
-  also be specified by giving an index into a small table of colors, the 
-  \code{\link{palette}}: indices wrap round so with the default palette 
-  of size 8, \code{10} is the same as \code{2}.  This provides 
-  compatibility with S.  Index \code{0} corresponds to the background 
+  also be specified by giving an index into a small table of colors, the
+  \code{\link{palette}}: indices wrap round so with the default palette
+  of size 8, \code{10} is the same as \code{2}.  This provides
+  compatibility with S.  Index \code{0} corresponds to the background
   color.  Note that the palette (apart from \code{0} which is per-device)
   is a per-session setting.