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+<p align=center>
+  AssertionError and AssertionResult classes.
+</p>
+
+<p align=center>
+  <a href="https://github.com/chaijs/assertion-error/actions">
+    <img
+      alt="build:?"
+      src="https://github.com/chaijs/assertion-error/actions/workflows/nodejs.yml/badge.svg"
+    />
+  </a><a href="https://www.npmjs.com/package/assertion-error">
+    <img
+      alt="downloads:?"
+      src="https://img.shields.io/npm/dm/assertion-error.svg"
+    />
+  </a><a href="">
+    <img
+      alt="devDependencies:none"
+      src="https://img.shields.io/badge/dependencies-none-brightgreen"
+    />
+  </a>
+</p>
+
+## What is AssertionError?
+
+Assertion Error is a module that contains two classes: `AssertionError`, which
+is an instance of an `Error`, and `AssertionResult` which is not an instance of
+Error.
+
+These can be useful for returning from a function - if the function "succeeds"
+return an `AssertionResult` and if the function fails return (or throw) an
+`AssertionError`.
+
+Both `AssertionError` and `AssertionResult` implement the `Result` interface:
+
+```typescript
+interface Result {
+  name: "AssertionError" | "AssertionResult";
+  ok: boolean;
+  toJSON(...args: unknown[]): Record<string, unknown>;
+}
+```
+
+So if a function returns `AssertionResult | AssertionError` it is easy to check
+_which_ one is returned by checking either `.name` or `.ok`, or check
+`instanceof Error`.
+
+## Installation
+
+### Node.js
+
+`assertion-error` is available on [npm](http://npmjs.org).
+
+```
+$ npm install --save assertion-error
+```
+
+### Deno
+
+`assertion_error` is available on
+[Deno.land](https://deno.land/x/assertion_error)
+
+```typescript
+import {
+  AssertionError,
+  AssertionResult,
+} from "https://deno.land/x/assertion_error@2.0.0/mod.ts";
+```