# API: Parser Integration API
### Scope
- **Purpose**: Define the public operations, token types, and transformation hooks for the single-pass parser integration layer.
- **Responsibility**: Contracts the observable behaviour callers depend on for the parser integration feature.
- **In Scope**: Parser entry point, token classification variants, transformation callback registration, iterator output.
- **Out of Scope**: Basic split API (`api/001`); string utility API (`api/002`); internal tokenizer implementation (`feature/008`).
### Operations
The parser integration API exposes a builder that accepts a source string and produces a classified, transformed token iterator.
The caller registers zero or more transformation callbacks before executing the parser. Each callback receives a mutable token and may modify its content. Callbacks are applied in registration order.
The iterator yields tokens in source order. Each token is classified as a delimited segment, a delimiter, or a structural boundary. Token content reflects any transformations applied.
The parser does not collect tokens into a container; it yields one token per call to `next`, keeping memory usage proportional to the largest single token rather than the entire source.
### Cross-References
| source | `src/string/parser.rs` | Parser, token types, and transformation pipeline |
| test | `tests/parser_integration_comprehensive_test.rs` | Parser API behaviour and transformation tests |
| doc | `docs/feature/008_parser_integration.md` | Parser integration feature design |