Encodings and how they're specified

Dear All

 

I'm trying to get clear in my head about how encodings are handled by XML parsers, it's something I've only ever half understood but feel I should know more.

I know that files can have a byte order mark at the start to help the parser decide how the document's encoded and then there's the encoding specified in the decalaration.

 

There's also encoding information available from elsewhere, HTTP headers etc.

 

Could someone explain step-by-step what happens when a parser opens a document, I still don't see how it manages to read the encoding mentioned in the XML declaration with only the BOM available?

Thanks

Joe