OOP approach to using DOMDocument
Some things I spot on the fly:


Lack of documentation. PHPDoc works well, every method, every class, every file should have a DocBlock.
Naming conventions. It's considered good naming convention to have methodNames() and $variableNames in camelCase, but ClassNames and ObjectNames in UppercaseCamelCase.
Code style. Conforming to a single code style is great. Conforming to an established standard is awesome!. Check out the PSR Code style standards page.
On the newElement method, preg_split is redundant. explode by ; or = is enough, and is faster!
Last but not least, if the entire file is PHP (without embedding HTML), it's considered safe (and even recommended!) to omit the closing ?&gt; at the end of the file. This helps with line break and whitespace issues.


I'll continue editing as I explore more.