add design philosophy and join_on_conjunctions note

Author: derek73

AGENTS.md

@@ -67,6 +67,8 @@ logging.getLogger('HumanName').setLevel(logging.DEBUG)
 
 The library has two layers: `nameparser/config/` (data) and `nameparser/parser.py` (logic).
 
+**Design philosophy — positional and language-agnostic.** The parser assigns parts by *position* plus small sets of words that join to neighbors; it never detects language. A name's language can't be reliably inferred from Latin-script transliteration ("Ali" is Arabic or Italian; "Van"/"Della"/"Bin" are first names in some cultures, particles in others), so language-specific rules belong in opt-in `Constants` config, never global defaults. Many "wrong for language X" reports (#133, #150, #130, #85, #103, #146, #83) are irreducible ambiguities — e.g. `de Mesnil` (want last name) vs `Van Johnson` (want first name) are the same `[prefix][word]` shape. Before adding a rule, confirm it doesn't break the opposite case (run the full suite — Portuguese and "Van Johnson" tests are the usual canaries).
+
 ### Configuration layer (`nameparser/config/`)
 
 Each module defines a plain Python set of known name pieces:
@@ -120,6 +122,8 @@ Each named attribute (`title`, `first`, etc.) is a `@property` that joins its co
 
 **`pr/NNN` local branches** track upstream PRs — don't commit to them by accident. Check `git branch --show-current` before starting work.
 
+**Prefix-join uses value-based `list.index()`** in `join_on_conjunctions` — fragile when a token value repeats (e.g. a trailing title that's also a suffix acronym, or two `van`s); constrain such lookups to start at `i + 1`. See #100.
+
 ### Tests (`tests/`)
 
 Tests run under **pytest** (via `uv run pytest`) and are split one file per concern (`tests/test_titles.py`, `tests/test_suffixes.py`, etc.). `tests/base.py` holds `HumanNameTestBase` — a plain (non-`unittest`) base whose `m()` helper is a custom assert that prints the original name string on failure (plus thin `assert*` shims so the moved test bodies are unchanged). `tests/conftest.py` defines an autouse fixture that runs **every test twice** — once with `empty_attribute_default = ''` and once with `None` — so reported counts are doubled (e.g. 11 methods → 22 results); it also snapshots/restores the scalar `CONSTANTS` config around each test to keep tests order-independent. `TEST_NAMES` (in `tests/test_variations.py`) is a list of name strings permuted into comma-separated variants as a regression check. Tests that should fail use `@pytest.mark.xfail`. When adding a parsing case, add it to the relevant `tests/test_*.py` file and consider adding the base form to `TEST_NAMES`.