$xml = new ArrayToXML();
print $xml->buildXML($input);

$input = array('product' => array(
'@id' => 7,
'name' => 'some string',
'seo' => 'some-string',
'ean' => '',
'producer' => array(
'name' => null,
'photo' => '1.png'
),
'stock' => 123,
'trackstock' => 0,
'new' => 0,
'pricewithoutvat' => 1111,
'price' => 1366.53,
'discountpricenetto' => null,
'discountprice' => null,
'vatvalue' => 23,
'currencysymbol' => 'PLN',
'#description' => '',
'#longdescription' => '',
'#shortdescription' => '',
'category' => array(
'photo' => '1.png',
'name' => 'test3',
),
'staticattributes' => array(
'attributegroup' => array(
1 => array(
'@name' => 'attributes group',
'attribute' => array(
0 => array(
'name' => 'second',
'description' => 'desc2',
'file' => '',
),
1 =>
array(
'name' => 'third',
'description' => 'desc3',
'file' => '',
),
)
)
)
),
'attributes' => array(),
'photos' => array(
'photo' => array(
0 => array(
'@mainphoto' => '1',
'%' => '1.png',
),
1 => array(
'@mainphoto' => '0',
'%' => '2.png',
),
2 => array(
'@mainphoto' => '0',
'%' => '3.png',
)
)
)
));

<"1.0" encoding="UTF-8""8">
<description><[CDATA[]]></description>
<longdescription><[CDATA[]]></longdescription>
<shortdescription><[CDATA[]]></shortdescription>
<name>some string</name>
<seo>some-string</seo>
<ean></ean>
<producer>
<name></name>
<photo>1.png</photo>
</producer>
<stock>123</stock>
<trackstock>0</trackstock>
<new>0</new>
<pricewithoutvat>1111</pricewithoutvat>
<price>1366.53</price>
<discountpricenetto></discountpricenetto>
<discountprice></discountprice>
<vatvalue>23</vatvalue>
<currencysymbol>PLN</currencysymbol>
<category>
<photo>1.png</photo>
<name>test3</name>
</category>
<staticattributes>
<attributegroup name="attributes group">
<attribute>
<name>second</name>
<description><p>desc2</p></description>
<file></file>
</attribute>
<attribute>
<name>third</name>
<description><p>desc3</p></description>
<file></file>
</attribute>
</attributegroup>
</staticattributes>
<photos>
<photo mainphoto="1">1.png</photo>
<photo mainphoto="0">2.png</photo>
<photo mainphoto="0">3.png</photo>
</photos>
</product>
</data>

$input = [
"key" =>[
"@id" => 1,
"!" => 2
]
]