The constuctor arguments are useful if you want to build a new document using createElement, appendChild etc.
By contrast, these arguments are overriden as soon as you load a document from source by calling load() or loadXML().
* If the source contains an XML declaration specifying an encoding, that encoding is used.
* If the XML declaration does not specify an encoding, or if the source does not contain a declaration at all, UTF-8 is assumed.
This behaviour applies no matter what you declared when you called new DOMDocument().
