Clarify USCC entity categories and validation limits

[zbl1998-sdjn]

The USCC module currently lists ownership and investment structures as examples of the second character's entity categories. This can lead readers to infer ownership from a prefix that instead encodes a category within a registering authority.

This documentation-only change lists the categories under authority 9, explains that the category must be read with the authority, and notes a current exception to inferring the present entity type from a retained code. It also makes the validation boundary explicit: formatting and checksum validation do not establish issuance or current registration.

Official references:

• Beijing Administration for Market Regulation: interpreting a USCC gives categories 1 (enterprise), 2 (individually-owned business), and 3 (farmers' specialised cooperative) under authority 9.
• SAMR Order No. 112, effective 1 February 2026, Article 10 says that an individually-owned business converting to an enterprise through a change of registration retains its unified social credit code.

Validation:

python -X utf8 -m doctest -o NORMALIZE_WHITESPACE -o IGNORE_EXCEPTION_DETAIL stdnum/cn/uscc.py tests/test_cn_uscc.doctest
git diff --check

Both checks passed. An AST comparison with docstrings removed also confirmed that executable code is unchanged. No validation rules or accepted-number behavior are changed.

Disclosure: this contribution was prepared with AI assistance while maintaining Currawong's USCI educational resources. The proposed corrections rely on the official references above.

[Copilot]

Copilot review overview

🔵 Needs a closer look

Authority 9 terminology remains inconsistent; update the earlier SAIC wording.

Review effort: Lite
Findings: None

What changed in this PR

Documentation-only clarification of USCC entity categories, retained codes, and validation limits.

Changes:

• Documents authority-9 categories and retained-code exceptions.
• Adds official references.
• Clarifies validation scope without changing executable behavior.

File	Summary
stdnum/​cn/​uscc.py	Updates module and validation documentation.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.