Clarify where the severity level is defined

[Kuwamura Masaki]

Hi,

Recently I read the document about ereport()[1].
Then, I felt that there is little information about severity level.
So I guess it can be kind to clarify where severity level is defined(see
attached patch please).

Any thoughts?


[1] https://www.postgresql.org/docs/devel/error-message-reporting.html

diff --git a/doc/src/sgml/sources.sgml b/doc/src/sgml/sources.sgml
index 514090d5a6..738fd3fe0c 100644
--- a/doc/src/sgml/sources.sgml
+++ b/doc/src/sgml/sources.sgml
@@ -105,7 +105,8 @@ less -x4
 
    <para>
     There are two required elements for every message: a severity level
-    (ranging from <literal>DEBUG</literal> to <literal>PANIC</literal>) and a 
primary
+    (ranging from <literal>DEBUG</literal> to <literal>PANIC</literal>, 
defined at
+    the top of <filename>src/include/utils/elog.h</filename>) and a primary
     message text.  In addition there are optional elements, the most
     common of which is an error identifier code that follows the SQL spec's
     SQLSTATE conventions.