--- a/libinterp/corefcn/regexp.cc	Sun Feb 25 21:20:56 2024 -0800
+++ b/libinterp/corefcn/regexp.cc	Mon Feb 26 23:30:33 2024 -0500
@@ -879,6 +879,13 @@
 searches that reduce the number of matches (e.g., by creatively using set
 complement), and then further processing the return variables (now reduced in
 size) with successive @code{regexp} searches.
+
+Octave's @code{regexp} implementaion is based on the Perl Compatible Regular 
+Expressions library (@url{https://www.pcre.org/}).  For a more comprehensive list
+of rexexp operator syntax see the 
+@url{https://www.pcre.org/current/doc/html/pcre2syntax.html,,
+"PCRE Syntax quick-reference summary"}.
+
 @seealso{regexpi, strfind, regexprep}
 @end deftypefn */)
 {