add $xmlStandalone as a new parameter

README.md

@@ -59,6 +59,7 @@ After running this piece of code `$result` will contain:
 </root>
 ```
 
+
 ### Setting the name of the root element
 
 Optionally you can set the name of the rootElement by passing it as the second argument. If you don't specify
@@ -159,6 +160,25 @@ This code will result in:
 
 If your input contains something that cannot be parsed a `DOMException` will be thrown.
 
+
+### Customize the XML declaration
+
+You could specify specific values in for:
+ - encoding as the fourth argument (string)
+ - version as the fifth argument (string)
+ - standalone as sixth argument (boolean)
+
+```php
+$result = ArrayToXml::convert($array, [], true, 'UTF-8', '1.1', [], true);
+```
+
+This will result in:
+
+```xml
+<?xml version="1.1" encoding="UTF-8" standalone="yes"?>
+```
+
+
 ### Adding attributes to the root element
 
 To add attributes to the root element provide an array with an `_attributes` key as the second argument. 

src/ArrayToXml.php

@@ -23,10 +23,15 @@ public function __construct(
         $replaceSpacesByUnderScoresInKeyNames = true,
         $xmlEncoding = null,
         $xmlVersion = '1.0',
-        $domProperties = []
+        $domProperties = [],
+        $xmlStandalone = null
     ) {
         $this->document = new DOMDocument($xmlVersion, $xmlEncoding);
 
+        if (! is_null($xmlStandalone)) {
+            $this->document->xmlStandalone = $xmlStandalone;
+        }
+
         if (! empty($domProperties)) {
             $this->setDomProperties($domProperties);
         }
@@ -55,15 +60,17 @@ public static function convert(
         bool $replaceSpacesByUnderScoresInKeyNames = true,
         string $xmlEncoding = null,
         string $xmlVersion = '1.0',
-        array $domProperties = []
+        array $domProperties = [],
+        bool $xmlStandalone = null
     ) {
         $converter = new static(
             $array,
             $rootElement,
             $replaceSpacesByUnderScoresInKeyNames,
             $xmlEncoding,
             $xmlVersion,
-            $domProperties
+            $domProperties,
+            $xmlStandalone
         );
 
         return $converter->toXml();

tests/ArrayToXmlTest.php

@@ -126,6 +126,12 @@ public function it_accepts_an_xml_version()
         $this->assertMatchesSnapshot(ArrayToXml::convert([], '', false, null, '1.1'));
     }
 
+    /** @test */
+    public function it_accepts_an_xml_standalone_value()
+    {
+        $this->assertMatchesSnapshot(ArrayToXml::convert([], '', false, null, '1.0', [], false));
+    }
+
     /** @test */
     public function it_can_handle_values_as_collection()
     {

tests/__snapshots__/ArrayToXmlTest__it_accepts_an_xml_standalone_value__1.php

@@ -0,0 +1,5 @@
+<?php
+
+return '<?xml version="1.0" standalone="no"?>
+<root/>
+';