* doc/groff.texinfo (Expressions): Improve documentation of `!'.

* tmac/trace.tmac (return): Don't call `substring'.

1 files changed, 4 insertions, 2 deletions

diff --git a/doc/groff.texinfo b/doc/groff.texinfo
index e4670ac4..05394f35 100644
--- a/doc/groff.texinfo
+++ b/doc/groff.texinfo
@@ -5088,8 +5088,10 @@ Logical: @samp{&} (logical and), @samp{:} (logical or).
 @cindex @code{while} request, and the @samp{!} operator
 Unary operators: @samp{-} (negating, i.e.@: changing the sign), @samp{+}
 (just for completeness; does nothing in expressions), @samp{!} (logical
-not; this works only within @code{if} and @code{while} requests).  See
-below for the use of unary operators in motion requests.
+not; this works only within @code{if} and @code{while}
+requests).@footnote{Note that, for example, @sample{!(-1)} evaluates to
+`true' because @code{gtroff} treats both negative numbers and zero as
+`false'.}  See below for the use of unary operators in motion requests.
 
 @item
 @cindex extremum operators (@code{>?}, @code{<?})