Fix GH-1164: strftime is deprecated since PHP 8.1

appendices/migration81/deprecated.xml

@@ -164,15 +164,21 @@ $arr[] = 2;
   <title>Date</title>
 
   <para>
-   The <function>date_sunrise</function> and <function>date_sunset</function>
+   <function>date_sunrise</function> and <function>date_sunset</function>
    have been deprecated in favor of <function>date_sun_info</function>.
   </para>
 
   <para>
-   The <function>strptime</function> has been deprecated.
+   <function>strptime</function> has been deprecated.
    Use <function>date_parse_from_format</function> instead (for locale-independent parsing),
    or <methodname>IntlDateFormatter::parse</methodname> (for locale-dependent parsing).
   </para>
+
+  <para>
+   <function>strftime</function> and <function>gmstrftime</function> have been deprecated.
+   Use <function>date</function> instead (for locale-independent parsing),
+   or <methodname>IntlDateFormatter::format</methodname> (for locale-dependent parsing).
+  </para>
  </sect2>
 
  <sect2 xml:id="migration81.deprecated.filter">

reference/datetime/functions/gmstrftime.xml

@@ -6,6 +6,10 @@
   <refpurpose>Format a GMT/UTC time/date according to locale settings</refpurpose>
  </refnamediv>
 
+ <refsynopsisdiv>
+  &warn.deprecated.function-8-1-0;
+ </refsynopsisdiv>
+
  <refsect1 role="description">
   &reftitle.description;
   <methodsynopsis>

reference/datetime/functions/strftime.xml

@@ -6,6 +6,10 @@
   <refpurpose>Format a local time/date according to locale settings</refpurpose>
  </refnamediv>
 
+ <refsynopsisdiv>
+  &warn.deprecated.function-8-1-0;
+ </refsynopsisdiv>
+
  <refsect1 role="description">
   &reftitle.description;
   <methodsynopsis>