The OPC is specified in Part 2 of the Office Open XML standards ISO/IEC 29500:2008 and ECMA-376 [REF].
The ISO/IEC 29500-2:2008 specification and the second edition of ECMA-376 makes a normative reference to PKWARE, Inc.'s .ZIP File Format Specification version 6.2.0 (2004), and supplements it with a normative set of clarifications.