The first layer of Uniword’s verification pipeline checks the Open Packaging Conventions (OPC) structure of DOCX files.

1. What OPC Checks

ZIP integrity (OPC-001)

Verifies that the file is a valid ZIP archive that can be opened without errors. Corrupted ZIP files fail at this stage.

Content types (OPC-002, OPC-003)

Validates that [Content_Types].xml exists, is well-formed XML, and correctly lists all parts in the package with their MIME types.

Relationships (OPC-005, OPC-006)

Checks that _rels/.rels and all per-part .rels files exist and reference valid targets. Every relationship target must resolve to an actual part within the package.

Part presence (OPC-004)

Verifies that required parts are present. At minimum, word/document.xml must exist in a valid DOCX file.

2. CLI Usage 

# OPC validation is included by default in verify
uniword verify document.docx

# Verbose output shows detailed OPC checks
uniword verify document.docx --verbose

3. Rule Codes

OPC rules use the OPC-xxx prefix:

Code Description

OPC-001

ZIP archive can be opened

OPC-002

Content types file is valid

OPC-003

Content types cover all parts

OPC-004

Required parts are present

OPC-005

Relationships are well-formed

OPC-006

Relationship targets resolve

4. Programmatic Usage 

require 'uniword'

result = Uniword::Verification.verify('document.docx')
opc_issues = result.issues.select { |i| i.code.start_with?('OPC-') }
opc_issues.each { |i| puts "#{i.code}: #{i.message}" }