Add a warning for FILTER_SANITIZE_NUMBER_FLOAT

This integrates user note 125563

Author: Girgias

reference/filter/constants.xml

@@ -1054,6 +1054,31 @@
       </listitem>
      </varlistentry>
     </variablelist>
+    <warning>
+     <simpara>
+      If the <constant>FILTER_FLAG_ALLOW_FRACTION</constant> flag is not used,
+      then the decimal separator is removed, altering the value received.
+     </simpara>
+     <informalexample>
+      <programlisting role="php">
+<![CDATA[
+<?php
+$number = '12.34';
+
+var_dump(filter_var($number, FILTER_SANITIZE_NUMBER_FLOAT));
+var_dump(filter_var($number, FILTER_SANITIZE_NUMBER_FLOAT, FILTER_FLAG_ALLOW_FRACTION));
+?>
+]]>
+      </programlisting>
+      &example.outputs;
+      <screen>
+<![CDATA[
+string(4) "1234"
+string(5) "12.34"
+]]>
+      </screen>
+     </informalexample>
+    </warning>
    </listitem>
   </varlistentry>