ZIm/crates/eval/examples/tax_id_validation/criteria.md

1. Documentation updates in README.md, where a new validation type for Employer Identification Numbers (EIN) was added to the supported validators table. This addition was carefully positioned between the existing "e164" phone number format and "email" validators to maintain alphabetical ordering. The entry follows the established table format with pipe-separated columns and includes a clear description indicating its purpose for validating U.S. Employer Identification Numbers. Notably, this change was made without modifying any of the existing documentation entries, preserving all current validator descriptions while expanding the supported validation types.
2. Core implementation of the EIN validation across multiple files. In baked_in.go, this involved adding an "ein" entry to the validator map that points to a newly created isEIN function, following the same pattern as other validator registrations. The isEIN() function itself implements the validation logic, checking for both length requirements (exactly 10 characters) and pattern matching using a new regular expression. The regexes.go file was updated with a new einRegexString constant defining the EIN pattern (##-#######) and corresponding regex variable initialization, utilizing the existing lazyRegexCompile helper function for consistency. Documentation was added in doc.go following the established format for validator descriptions, complete with a simple usage example. Throughout these changes, careful attention was paid to maintain consistent error handling patterns and code organization while removing unnecessary newlines in several functions to improve readability.
3. Testing improvements and code quality enhancements, primarily in validator_test.go. A comprehensive TestEINStringValidation test case was added, covering various valid and invalid EIN formats, including tests for length requirements and hyphen positioning. This new test follows the same structure and assertion patterns as existing validation tests. Numerous code quality improvements were made throughout the test file, including grouping interface declarations, fixing comment formatting, removing unnecessary newlines in struct declarations, correcting indentation in test cases, and adding missing newlines between tests. These changes significantly improved code readability while maintaining all existing test logic and ensuring backward compatibility. The improvements demonstrate careful attention to maintaining consistent patterns throughout the test suite while adding thorough test coverage for the new EIN validation functionality.