How DOMError operates?

Hello everyone!

I have some questions on DOMError (and DOMLocator)...
I would want to know when DOMError is used.
In the DOMError object location is a DOMLocator object but i don't understand
if DOMLocator Uri is the document Uri and how to define UTF16 and Byte
offset.
What are the DOMError and DOMLocator constructors?

Thanks,

Max