The following clarifying note and recommendation have been added to section 10.1 of the XPS specification in regard different methods of parsing the ZIP-based package that is the foundation of the XPS Document.
Note: Consumers can choose to parse an XPS Document in a head-first or tail-first manner. Tail-first parsing reveals certain package errors earlier, such as inconsistencies between the ZIP central directory and local file headers. Head-first XPS Document consumers SHOULD attempt to detect inconsistent packages as soon as possible and SHOULD generate an error message, even if they have already processed the pages that resulted in the error [S10.18]. Head-first consumers that discard parts would need to retain the name and length of any discarded part to comply with this recommendation.