bug#38026: [PATCH] Explain negative NABS in `goto-history-element'.

[Hong Xu <hong@topbug.net>]

* doc/lispref/minibuf.texi (Minibuffer Commands): Explain negative NABS.

* lisp/simple.el (goto-history-element): Explain negative NABS.
---
 doc/lispref/minibuf.texi | 5 +++++
 lisp/simple.el           | 7 ++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/doc/lispref/minibuf.texi b/doc/lispref/minibuf.texi
index d36babd69873..a9bb3aec9583 100644
--- a/doc/lispref/minibuf.texi
+++ b/doc/lispref/minibuf.texi
@@ -2339,6 +2339,11 @@ Minibuffer Commands
 minibuffer.  The argument @var{nabs} specifies the absolute history
 position in descending order, where 0 means the current element and a
 positive number @var{n} means the @var{n}th previous element.
+
+@{nabs} being a negative number @var{n} means the @var{n-1}th element
+of @code{minibuffer-default} if it is a list, or otherwise the value
+of @code{minibuffer-default}.  This is usually an intelligent guess of
+what the user intends to input."
 @end deffn
 
 @node Minibuffer Windows
diff --git a/lisp/simple.el b/lisp/simple.el
index 10aecd651f39..e95e2bc22972 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -2130,7 +2130,12 @@ goto-history-element
   "Puts element of the minibuffer history in the minibuffer.
 The argument NABS specifies the absolute history position in
 descending order, where 0 means the current element and a
-positive number N means the Nth previous element."
+positive number N means the Nth previous element.
+
+NABS being a negative number N means the (N-1)th element of
+`minibuffer-default' if it is a list, or otherwise the value of
+`minibuffer-default'.  This is usually an intelligent guess of
+what the user intends to input."
   (interactive "p")
   (when (and (not minibuffer-default-add-done)
 	     (functionp minibuffer-default-add-function)
-- 
2.20.1