1 files changed, 13 insertions, 1 deletions

diff --git a/doc/lispref/lists.texi b/doc/lispref/lists.texi
index f3758f5ce60..911defbc211 100644
--- a/doc/lispref/lists.texi
+++ b/doc/lispref/lists.texi
@@ -705,9 +705,21 @@ same way.
 Normally, when @var{tree} is anything other than a cons cell,
 @code{copy-tree} simply returns @var{tree}.  However, if @var{vecp} is
 non-@code{nil}, it copies vectors too (and operates recursively on
-their elements).
+their elements).  This function cannot cope with circular lists.
 @end defun
 
+@defun safe-copy-tree tree &optional vecp
+This function returns a copy of the tree @var{tree}.  If @var{tree} is
+a cons cell, this make a new cons cell with the same @sc{car} and
+@sc{cdr}, then recursively copies the @sc{car} and @sc{cdr} in the
+same way.
+
+Normally, when @var{tree} is anything other than a cons cell,
+@code{copy-tree} simply returns @var{tree}.  However, if @var{vecp} is
+non-@code{nil}, it copies vectors and records too (and operates
+recursively on their elements).  This function handles circular lists
+and vectors, and is thus slower than @code{copy-tree} for typical cases.
+
 @defun flatten-tree tree
 This function returns a ``flattened'' copy of @var{tree}, that is,
 a list containing all the non-@code{nil} terminal nodes, or leaves, of