📝 Document matcher caveats in the README

State the end-user limits once, in README § Caveats: a member colliding
with its stringification, the unsupported symbol/bigint, and NaN/-0. Drop
the duplicated known-issue prose from development/library.md and the
source comment; link to the README instead.

README.md

@@ -9,7 +9,7 @@ ordinary objects whose `matches` method is a TypeScript type guard, so narrowing
 composes the way any other guard does. It is deliberately not a regex engine and
 not a macro: there is no transpiler and no DSL to learn, and the type-level
 contract is the feature — see [development/library.md](./development/library.md)
-for the design decisions and the known limitations.
+for the design decisions and [Caveats](#caveats) for the limits.
 
 ## Requirements
 
@@ -23,6 +23,18 @@ for the design decisions and the known limitations.
 
 Yet to be implemented
 
+## Caveats
+
+- **A value and its stringification collide.** Object keys stringify, so a
+  universe that mixes a member with the string it stringifies to — `1 | "1"`,
+  `true | "true"`, `null | "null"` — collapses to a single handler key and both
+  members are routed to it. Use one form or the other.
+- **`symbol` and `bigint` are not supported.** A `symbol` brand is a
+  compile-time phantom with nothing to match at runtime, and a `bigint` is not a
+  valid property key; neither satisfies the matcher's universe constraint.
+- **`NaN` and `-0` cannot be matched specifically.** They have no literal type,
+  so both stay part of `number`.
+
 ## License
 
 MIT © 2025 tmu. See [LICENSE](./LICENSE).

development/library.md

@@ -97,7 +97,7 @@ Each factory is two overloads whose order is load-bearing:
 #### Decision (2026-09)
 
 The universe (`Matchable`) is `string | number | boolean | null | undefined`,
-with `boolean` admitted as `true | false`. `symbol` and `bigint` are not.
+with `boolean` admitted as `true | false`.
 
 `boolean`/`null`/`undefined` are not property keys, so handler-map keys are a
 projection (`PatternKey`: each member stringified) and `PatternParam` inverts
@@ -109,18 +109,6 @@ offers `true`, `false`, `null`, `undefined` by name (verified over LSP).
 - Runtime dispatch is unchanged in effect: `handlers[true]` already coerces to
   `"true"`. `dispatch` wraps the index in `String()` only because TypeScript
   forbids indexing with `boolean`/`null`/`undefined` (`TS2538`).
-
-#### Rejected
-
-- **`symbol`.** A brand is a compile-time phantom — nothing to match at
-  runtime; the popup cannot offer symbol keys anyway.
-- **`bigint`.** Not a valid property key; a stringified key (`"1"`) collides
-  with numeric `1`.
-- **`NaN` / `-0`.** No literal type exists; they stay one `number`.
-
-#### Known issue
-
-- A universe mixing a member with its stringification (`1 | "1"`,
-  `true | "true"`, `null | "null"`) collapses to one handler key and routes
-  both members to it. Pre-existing for `1 | "1"`; now reachable for the new
-  members. Not guarded at the type level.
+- `symbol`/`bigint`/`NaN`/`-0` are rejected, and a member colliding with its
+  stringification is unguarded: user-facing, stated once in
+  [README § Caveats](../README.md#caveats).

src/primitive.ts

@@ -3,16 +3,13 @@ import type { Exact, ValueOf } from "type-fest";
 type UnaryFn<T, R> = (shape: T) => R;
 
 // The primitive universe a matcher can discriminate. `boolean` is admitted as
-// the pair `true | false`; `symbol` is deliberately absent (a brand is a
-// compile-time phantom, so there is nothing to match at runtime).
+// the pair `true | false`; see README § Caveats for the unsupported members.
 type Matchable = string | number | boolean | null | undefined;
 
 // `boolean`, `null` and `undefined` cannot be property keys, so a mapped type
 // over the universe keys each non-key member by its stringification. `Param`
 // inverts that projection, so a handler callback still receives the *real*
-// member (`true`, not `"true"`). A universe mixing a member with the string it
-// stringifies to (e.g. `true | "true"`) collapses to one key and is not
-// representable — see development/library.md.
+// member (`true`, not `"true"`) — see README § Caveats for the limits.
 type PatternKey<T> = T extends boolean
     ? T extends true
         ? "true"