I have been working on a REST API using the excellent tools provided by Yii2. My problem was that I have to differentiate between empty values and null values. In other words, <elem></elem> is different from null as it represents an empty string. Also, although some use <elem/> to represent a null value it should still be interpreted as an empty string. In other cases, the absence of the element is taken to represent a null value, but this may create problem with some parsers.
By Integrating the Zend 2.* framework into Yii you can quickly and painlessly generate XML outputs from your controllers. This will be helpful to anyone who has never done this before or only done it with Zend 1 as the introduction of namespaces can be strange when you first view them.