Fix #79111: is_numeric documentation utterly incomplete

We add information about leading and trailing whitespace.

Co-authored-by: Christoph M. Becker <[email protected]>

Closes GH-870.

Author: deleugpn

reference/var/functions/is-numeric.xml

@@ -104,6 +104,73 @@ NULL is NOT numeric
     </screen>
    </example>
   </para>
+
+  <para>
+   <example>
+    <title><function>is_numeric</function> with whitespace</title>
+    <programlisting role="php">
+     <![CDATA[
+<?php
+$tests = [
+    " 42",
+    "42 ",
+    " 9001", // non-breaking space
+    "9001 ", // non-breaking space
+];
+
+foreach ($tests as $element) {
+    if (is_numeric($element)) {
+        echo var_export($element, true) . " is numeric", PHP_EOL;
+    } else {
+        echo var_export($element, true) . " is NOT numeric", PHP_EOL;
+    }
+}
+?>
+]]>
+    </programlisting>
+    &example.outputs.8;
+    <screen>
+     <![CDATA[
+' 42' is numeric
+'42 ' is numeric
+' 9001' is NOT numeric
+'9001 ' is NOT numeric
+]]>
+    </screen>
+    &example.outputs.7;
+    <screen>
+     <![CDATA[
+' 42' is numeric
+'42 ' is NOT numeric
+' 9001' is NOT numeric
+'9001 ' is NOT numeric
+]]>
+    </screen>
+   </example>
+  </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>
+       Numeric strings ending with whitespace (<literal>"42 "</literal>) will now
+       return &true;. Previously, &false; was return instead.
+      </entry>
+     </row>
+    </tbody>
+   </tgroup>
+  </informaltable>
  </refsect1>
 
  <refsect1 role="seealso">