> previous editions... used a sliver of the resources

Well of course, but given that the previously employed technique was blitting, fliedumping memory areas, you can't be more efficient than that. Using XML is for transparency (readability).

(And, note, in context, I regard the ms office file format as lousy. The OpenOffice/LibreOffice format is good.)

I don't think your parent comment was talking about the resources involved in saving a file, but rather the resources involved in running the software.