docs: improve old() description

user_guide_src/source/general/common_functions.rst

@@ -79,7 +79,7 @@ Service Accessors
     If $data is a string, then it simply escapes and returns it.
     If $data is an array, then it loops over it, escaping each 'value' of the key/value pairs.
 
-    Valid context values: html, js, css, url, attr, raw
+    Valid context values: ``html``, ``js``, ``css``, ``url``, ``attr``, ``raw``
 
 .. php:function:: helper($filename)
 
@@ -117,19 +117,21 @@ Service Accessors
 .. php:function:: old($key[, $default = null,[, $escape = 'html']])
 
     :param string $key: The name of the old form data to check for.
-    :param mixed  $default: The default value to return if $key doesn't exist.
-    :param mixed  $escape: An `escape <#esc>`_ context or false to disable it.
+    :param string|null  $default: The default value to return if $key doesn't exist.
+    :param false|string  $escape: An `escape <#esc>`_ context or false to disable it.
     :returns: The value of the defined key, or the default value.
-    :rtype: mixed
+    :rtype: array|string|null
 
     Provides a simple way to access "old input data" from submitting a form.
 
     Example:
 
     .. literalinclude:: common_functions/002.php
 
-.. note:: If you are using the :doc:`form helper </helpers/form_helper>`, this feature is built-in. You only
-        need to use this function when not using the form helper.
+.. note:: If you are using the :php:func:`set_value()`, :php:func:`set_select()`,
+    :php:func:`set_checkbox()`, and :php:func:`set_radio()` functions in
+    :doc:`form helper </helpers/form_helper>`, this feature is built-in. You only
+    need to use this function when not using the form helper.
 
 .. php:function:: session([$key])
 

user_guide_src/source/general/common_functions/002.php

@@ -2,8 +2,7 @@
 
 // in controller, checking form submittal
 if (! $model->save($user)) {
-    // 'withInput' is what specifies "old data"
-    // should be saved.
+    // 'withInput()' is what specifies "old data" should be saved.
     return redirect()->back()->withInput();
 }