diff --git a/framework/yii/i18n/Formatter.php b/framework/yii/i18n/Formatter.php
index d688a15..4a93397 100644
--- a/framework/yii/i18n/Formatter.php
+++ b/framework/yii/i18n/Formatter.php
@@ -30,19 +30,28 @@ class Formatter extends \yii\base\Formatter
 	 */
 	public $locale;
 	/**
-	 * @var string the default format string to be used to format a date using PHP date() function.
+	 * @var string the default format string to be used to format a date.
+	 * This can be "short", "medium", "long", or "full", which represents a preset format of different lengths.
+	 * It can also be a custom format as specified in the [ICU manual](http://userguide.icu-project.org/formatparse/datetime).
 	 */
 	public $dateFormat = 'short';
 	/**
-	 * @var string the default format string to be used to format a time using PHP date() function.
+	 * @var string the default format string to be used to format a time.
+	 * This can be "short", "medium", "long", or "full", which represents a preset format of different lengths.
+	 * It can also be a custom format as specified in the [ICU manual](http://userguide.icu-project.org/formatparse/datetime).
 	 */
 	public $timeFormat = 'short';
 	/**
-	 * @var string the default format string to be used to format a date and time using PHP date() function.
+	 * @var string the default format string to be used to format a date and time.
+	 * This can be "short", "medium", "long", or "full", which represents a preset format of different lengths.
+	 * It can also be a custom format as specified in the [ICU manual](http://userguide.icu-project.org/formatparse/datetime).
 	 */
 	public $datetimeFormat = 'short';
 	/**
 	 * @var array the options to be set for the NumberFormatter objects. Please refer to
+	 * [PHP manual](http://php.net/manual/en/class.numberformatter.php#intl.numberformatter-constants.unumberformatattribute)
+	 * for the possible options. This property is used by [[createNumberFormatter]] when
+	 * creating a new number formatter to format decimals, currencies, etc.
 	 */
 	public $numberFormatOptions = array();
 
@@ -81,8 +90,11 @@ class Formatter extends \yii\base\Formatter
 	 * - a PHP DateTime object
 	 *
 	 * @param string $format the format used to convert the value into a date string.
-	 * If null, [[dateFormat]] will be used. The format string should be the one
-	 * that can be recognized by the PHP `date()` function.
+	 * If null, [[dateFormat]] will be used.
+	 *
+	 * This can be "short", "medium", "long", or "full", which represents a preset format of different lengths.
+	 * It can also be a custom format as specified in the [ICU manual](http://userguide.icu-project.org/formatparse/datetime).
+	 *
 	 * @return string the formatted result
 	 * @see dateFormat
 	 */
@@ -111,8 +123,11 @@ class Formatter extends \yii\base\Formatter
 	 * - a PHP DateTime object
 	 *
 	 * @param string $format the format used to convert the value into a date string.
-	 * If null, [[dateFormat]] will be used. The format string should be the one
-	 * that can be recognized by the PHP `date()` function.
+	 * If null, [[dateFormat]] will be used.
+	 *
+	 * This can be "short", "medium", "long", or "full", which represents a preset format of different lengths.
+	 * It can also be a custom format as specified in the [ICU manual](http://userguide.icu-project.org/formatparse/datetime).
+	 *
 	 * @return string the formatted result
 	 * @see timeFormat
 	 */
@@ -141,8 +156,11 @@ class Formatter extends \yii\base\Formatter
 	 * - a PHP DateTime object
 	 *
 	 * @param string $format the format used to convert the value into a date string.
-	 * If null, [[dateFormat]] will be used. The format string should be the one
-	 * that can be recognized by the PHP `date()` function.
+	 * If null, [[dateFormat]] will be used.
+	 *
+	 * This can be "short", "medium", "long", or "full", which represents a preset format of different lengths.
+	 * It can also be a custom format as specified in the [ICU manual](http://userguide.icu-project.org/formatparse/datetime).
+	 *
 	 * @return string the formatted result
 	 * @see datetimeFormat
 	 */
@@ -213,7 +231,7 @@ class Formatter extends \yii\base\Formatter
 	/**
 	 * Creates a number formatter based on the given type and format.
 	 * @param integer $type the type of the number formatter
-	 * @param string $format the format to be used
+	 * @param string $format the format to be used.  Please refer to [ICU manual](http://www.icu-project.org/apiref/icu4c/classDecimalFormat.html#_details)
 	 * @return NumberFormatter the created formatter instance
 	 */
 	protected function createNumberFormatter($type, $format)