Fix GH-1182: constant() throws Error exception as of PHP 8.0.0

reference/misc/functions/constant.xml

@@ -46,19 +46,43 @@
  <refsect1 role="returnvalues">
   &reftitle.returnvalues;
   <para>
-   Returns the value of the constant, or &null; if the constant is not
-   defined.
+   Returns the value of the constant.
   </para>
  </refsect1>
 
  <refsect1 role="errors">
   &reftitle.errors;
   <para>
-   An <constant>E_WARNING</constant> level error is generated if the
-   constant is not defined.
+   An <classname>Error</classname> exception is thrown,
+   if the constant is not defined. Prior to PHP 8.0.0,
+   an <constant>E_WARNING</constant> level error was generated in that case.
   </para>
  </refsect1>
 
+ <refsect1 role="changelog">
+  &reftitle.changelog;
+  <informaltable>
+   <tgroup cols="2">
+    <thead>
+     <row>
+      <entry>&Version;</entry>
+      <entry>&Description;</entry>
+     </row>
+    </thead>
+    <tbody>
+     <row>
+      <entry>8.0.0</entry>
+      <entry>
+       If the constant is not defined, <function>constant</function> now throws an
+       <classname>Error</classname> exception; previously an <constant>E_WARNING</constant>
+       was generated, and &null; was returned.
+      </entry>
+     </row>
+    </tbody>
+   </tgroup>
+  </informaltable>
+ </refsect1>
+
  <refsect1 role="examples">
   &reftitle.examples;
   <para>