Add feature flags documentation

docs/compatibility.md

@@ -1,5 +1,96 @@
 # Compatibility
 
+All serialization methods can accept a `{ disabledFeatures: number }` option. This option influences how the serialization will process and emit a value.
+
+```js
+import { serialize, Feature } from 'seroval';
+
+const y = Object.create(null);
+y.self = y;
+y.example = 'Hello World';
+
+function serializeWithTarget(value, disabledFeatures) {
+  const result = serialize(value, {
+    disabledFeatures,
+  });
+  console.log(result);
+}
+
+serializeWithTarget(y, Feature.ArrowFunction | Feature.ObjectAssign);
+serializeWithTarget(y, 0);
+```
+
+```js
+(function(h){return (h=Object.create(null),h.self=h,h.example="Hello World",h)})()
+(h=>(h=Object.assign(Object.create(null),{example:"Hello World"}),h.self=h,h))()
+```
+
+`disabledFeatures` uses bit flags for faster checking, so if you need to disable multiple features, you can use the bitwise OR symbol (`|`).
+
+Here's an `ES2017` flag:
+
+```js
+import { serialize, Feature } from 'seroval';
+
+const ES2017FLAG = 
+  Feature.AggregateError // ES2021
+  | Feature.BigInt // ES2020
+  | Feature.BigIntTypedArray // ES2020;
+
+serialize(myValue, {
+  disabledFeatures: ES2017FLAG,
+})
+```
+
+By default, all feature flags are enabled. The following are the feature flags and their behavior when disabled:
+
+- [`AggregateError`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/AggregateError)
+  - Compiles down to `Error` instead.
+- [`ArrayPrototypeValues`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/values)
+  - Used for `Iterable`, uses `Symbol.iterator` instead.
+- [`ArrowFunction`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions)
+  - Uses function expressions for top-level and for deferred `Promise` values
+  - method shorthands (if `MethodShortand` is not set) or function expressions for `Iterable`.
+- [`BigInt`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
+  - Throws when attempted to use, includes `BigIntTypedArray`
+  - Disables use of `BigInt`, `BigInt64Array` and `BigUint64Array`
+- [`ErrorPrototypeStack`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/stack)
+  - Skipped when detected.
+  - Affects both `Error` and `AggregateError`
+- [`Map`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map)
+  - Throws when attempted to use.
+  - Disables serialization of `Map`
+- [`MethodShorthand`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Method_definitions)
+  - Uses function expressions instead.
+  - Only affects `Iterable`
+- [`ObjectAssign`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign)
+  - Uses manual object assignments instead.
+  - Affects `Iterable`, `Error`, `AggregateError` and `Object.create(null)`
+- [`Promise`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
+  - Throws when attempted to use in `serializeAsync` and `toJSONAsync`.
+  - Disables serialization of `Promise`
+- [`Set`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set)
+  - Throws when attempted to use.
+  - Disables serialization of `Set`
+- [`Symbol`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol)
+  - Throws when attempted to use.
+  - This disables serialization of well-known symbols and `Iterable`.
+- [`TypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray)
+  - Throws when attempted to use.
+  - Disables serialization of `TypedArray`
+- [`BigIntTypedArray`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt64Array)
+  - Throws when attempted to use
+  - Also throws if `BigInt` is disabled.
+  - Disables serialization of `BigInt64Array` and `BigUint64Array`
+- `WebAPI`
+  - Throws and disables the following usage:
+    - [`URL`](https://developer.mozilla.org/en-US/docs/Web/API/URL)
+    - [`URLSearchParams`](https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams)
+    - [`Blob`](https://developer.mozilla.org/en-US/docs/Web/API/Blob)
+    - [`File`](https://developer.mozilla.org/en-US/docs/Web/API/File)
+    - [`Headers`](https://developer.mozilla.org/en-US/docs/Web/API/Headers)
+    - [`FormData`](https://developer.mozilla.org/en-US/docs/Web/API/FormData)
+
 ## Supported Types
 
 - sync = `serialize`, `toJSON`, `crossSerialize`, `toCrossJSON`