Update README and CLAUDE.md

README: add --print-layout / -p flag to both command synopses and usage examples.

CLAUDE.md: document the trait conventions for domain types (Display = ZMK,
qmk_name() for QMK, From<&str> for mixed-format parsing), note that ToZmk/ToQmk
were removed and must not be reintroduced, and add the cmp_owned allow exception
for KeyExpr's PartialEq impls.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Patrick Carroll

CLAUDE.md

@@ -44,7 +44,10 @@ examples/
 
 All code must pass `cargo clippy --all-targets -- -W clippy::pedantic -D warnings` with no errors. This is enforced by CI. Run it locally before committing.
 
-The one deliberate exception is `#[allow(clippy::implicit_hasher)]` on `parse_key_expr_str` — threading separate hasher type parameters through all private helpers adds noise without value for a CLI tool.
+Deliberate exceptions:
+
+- `#[allow(clippy::implicit_hasher)]` on `parse_key_expr_str` — threading separate hasher type parameters through all private helpers adds noise without value for a CLI tool.
+- `#[allow(clippy::cmp_owned)]` on `KeyExpr`'s `PartialEq<&str>` / `PartialEq<str>` impls — the `Modified` variant (nested modifier expressions like `LG(LS(LBKT))`) must build a formatted string to compare; there is no allocation-free alternative.
 
 ## Testing
 
@@ -77,6 +80,18 @@ all of these are done and verified:
 9. Report the pushed commit, pushed tag, GitHub Release workflow status, and
    crates.io version.
 
+## Trait conventions for domain types
+
+The typed domain types in `src/codes.rs` (`KeyCode`, `Modifier`, `KeyExpr`, `RgbAction`, `MouseMovement`, `MouseButton`, `MouseScroll`, `ModPrefix`) follow a consistent pattern:
+
+- **`Display`** outputs the **ZMK** spelling. This is the canonical string form; use `.to_string()` or format interpolation `{x}` wherever a ZMK string is needed.
+- **`qmk_name()` / `qmk_mod_name()`** methods return the **QMK** spelling as `&str`. Call these directly in QMK renderers; do not add a trait wrapper.
+  - `Modifier` exposes three QMK spellings: `qmk_mod_name()` (`MOD_LSFT`, used in `MT`/`OSM`), `qmk_fn_name()` (`LSFT`, used in modifier-wrapping functions), and `zmk_name()` via `Display`.
+  - `KeyExpr` has a `to_qmk() -> String` method for the recursive modifier-expression case (e.g. `LGUI(LSFT(KC_LBRC))`).
+- **`From<&str>` / `From<String>`** are implemented for types with an `Unknown` fallback variant. They try ZMK spelling first, then QMK, then fall back to `Unknown(raw)`. Use these when the source format is ambiguous or mixed.
+- **`from_qmk(s)` / `from_zmk(s)`** associated functions return `Option<Self>` for strict format-specific parsing (no `Unknown` fallback). Prefer these in parsers where the input format is known.
+- There are **no custom `ToZmk` or `ToQmk` traits**. Earlier versions had them; they were removed because `Display` already covers the ZMK case and the QMK case has no stdlib equivalent. Don't reintroduce them.
+
 ## Key mapping conventions
 
 QMK and ZMK use different names for the same physical keys. The canonical mapping lives in `src/codes.rs`. Notable differences:

README.md

@@ -46,6 +46,7 @@ Options:
       --cols <COLS>          Override columns per row in ZMK output
       --list-keyboards       List known keyboards and their column counts, then exit
       --no-warn              Suppress warnings for unmapped keycodes
+  -p, --print-layout         Parse the keymap and print a layout table, then exit
   -h, --help                 Print help
 ```
 
@@ -68,6 +69,9 @@ qmk2zmk keymap.c --cols 10
 # List known keyboards
 qmk2zmk --list-keyboards
 
+# Print a human-readable layout table without converting
+qmk2zmk keymap.c --print-layout
+
 # Explicit format flag
 qmk2zmk -f json keymap.json -o my_keymap.keymap
 ```
@@ -88,6 +92,7 @@ Options:
       --cols <COLS>          Override columns per row in QMK C output
       --list-keyboards       List known keyboards and their column counts, then exit
       --no-warn              Suppress warnings for unmapped keycodes
+  -p, --print-layout         Parse the keymap and print a layout table, then exit
   -h, --help                 Print help
 ```
 
@@ -106,6 +111,9 @@ zmk2qmk my_keymap.keymap -f c --keyboard corne
 
 # List known keyboards
 zmk2qmk --list-keyboards
+
+# Print a human-readable layout table without converting
+zmk2qmk my_keymap.keymap --print-layout
 ```
 
 ## What gets converted