2.1.2 Part
A part is a stream of bytes as specified in [ISO/IEC29500-2:2012]: Open Packaging Conventions, section 8.2. Each part has an associated content type that specifies the nature and type of content stored in the part. Some parts store information using binary records (section 2.1.4). Some parts store information using XML.
The valid parts, content types, and required and optional relationships (section 2.1.3) between all parts in a package (section 2.1.1) are specified in Part Enumeration (section 2.1.7). Each part that contains binary records (section 2.1.4) MUST be written as a series of binary records as specified in Part Enumeration.
This document uses Augmented Backus-Naur Form (ABNF) as specified in [RFC5234] to specify the record (section 2.1.4) sequence for parts that contain binary records.