SimpleXML and mixed, nested namespaces

I work with several third party marketplace APIs, one of which is Amazon's MWS API.
When processing their GetMatchingProductForId response I discovered that they sometimes namespace the XML nodes (with ns2).

PHP's SimpleXML doesn't allow access to namespaced nodes via the usual interface of $simpleXml->node but I found you can specify a namespace to the children() method like so:

$simpleXml
    ->children('ns2', true)
    ->namespacedNode

That works great but then I hit a problem. As I mentioned, Amazon namespace some of the nodes but not all and the node I was really after was not namespaced itself but was a child of a namespaced node. After I applied the code above I found that I couldn't access the child node:

$simpleXml
    ->children('ns2', true)
    ->namespacedNode
    ->nonNamespacedNode

I thought all was lost until I discovered you can reset SimpleXML's namespace filter back to none again with another call to children() so you can get at the non-namespaced child node:

$simpleXml
    ->children('ns2', true)
    ->namespacedNode
    ->children()
    ->nonNamespacedNode

SimpleXML and large files

I encountered an issue earlier today whilst trying to process a fairly large (~37MB) XML file through SimpleXML.

It worked just fine on mine and a colleague's development systems but failed with weird errors on the live server, for instance reporting there was "Extra content at the end of the document".

After about an hour of trying to figure it out we realised our dev systems were using libxml v2.6.x and the live server was using 2.7.6. We then read that somewhere between those versions some hard-coded limits were added in that can cause the problem we were seeing.

To get around it you need to specify the LIBXML_PARSEHUGE flag:

$simplexml = simplexml_load_file($file_path, 'SimpleXMLElement', LIBXML_PARSEHUGE);
//OR
$simplexml = new SimpleXMLElement($xml_string, LIBXML_PARSEHUGE);