Merge pull request #42 from galvao/2.16.x

Adding details about the second parameter for Laminas\Log\Formatter\Simple, the DateTime object format

docs/book/formatters.md

@@ -32,12 +32,18 @@ $logger->info('there');
 // outputs "hello there"
 ```
 
-The constructor of `Laminas\Log\Formatter\Simple` accepts a single parameter: the
-format string. This string contains keys surrounded by percent signs (e.g.
-`%message%`). The format string may contain any key from the event data array.
+The constructor of `Laminas\Log\Formatter\Simple` accepts two parameters: the
+format string and the format for DateTime objects in event data. The format
+string contains keys surrounded by percent signs (e.g.
+`%message%`) and may contain any key from the event data array.
 You can retrieve the default keys by using the `DEFAULT_FORMAT` constant from
 `Laminas\Log\Formatter\Simple`.
 
+The DateTime format string follows PHP's [DateTimeInterface::format](https://www.php.net/manual/en/datetime.format.php)
+pattern and defaults to the format described in [ISO 8601](https://en.wikipedia.org/wiki/ISO_8601). You can
+retrieve the default DateTime format by using the
+`DEFAULT_DATETIME_FORMAT` constant from `Laminas\Log\Formatter\FormatterInterface`.
+
 ## Formatting to JSON
 
 `Laminas\Log\Formatter\Json` is the JSON formatter.  By default, it