|The DOMImplementation class is description of a particular
implementation of the Document Object Model. As such its data is
static, shared by all instances of this implementation.
The DOM API requires that it be a real object rather than static
methods. However, there's nothing that says it can't be a singleton,
so that's how I've implemented it.
This particular class, along with DocumentImpl, supports the DOM
Core, DOM Level 2 optional mofules, and Abstract Schemas (Experimental).