Document new error symbol and function user-error

* doc/lispref/control.texi (Signaling Errors):
* doc/lispref/debugging.texi (Error Debugging):
* doc/lispref/errors.texi (Standard Errors): Add user-error.

* etc/NEWS: Related markup.

1 files changed, 3 insertions, 0 deletions

diff --git a/doc/lispref/errors.texi b/doc/lispref/errors.texi
index a57f74d6c86..b92fd9ed665 100644
--- a/doc/lispref/errors.texi
+++ b/doc/lispref/errors.texi
@@ -172,6 +172,9 @@ The message is @samp{Text is read-only}.  This is a subcategory of
 @item undefined-color
 The message is @samp{Undefined color}.  @xref{Color Names}.
 
+@item user-error
+The message is the empty string.  @xref{Signaling Errors}.
+
 @item void-function
 The message is @samp{Symbol's function definition is void}.
 @xref{Function Cells}.