diff --git a/README.md b/README.md
index 6eb0171c..28ee11fe 100644
--- a/README.md
+++ b/README.md
@@ -110,6 +110,8 @@ The main module's default export is a class which you can construct with a few o
 - `implSuffix`: a suffix used, if any, to find files within the source directory based on the IDL file name
 - `suppressErrors`: set to true to suppress errors during generation
 - `processCEReactions` and `processHTMLConstructor`: see below
+- `processReflect`: see below
+- `importedTypes`: see below
 
 The `addSource()` method can then be called multiple times to add directories containing `.webidl` IDL files and `.js` implementation class files.
 
@@ -240,6 +242,27 @@ function processReflect(idl, implName) {
 }
 ```
 
+### `importedTypes`
+
+The `importedTypes` option takes a `record<string, string>` parameter, where keys are the names of Web IDL types, and the values are the path to the wrapper class API.
+
+In case where a single module exports multiple webidl2js interface wrappers under different namespaces, it's possible to use the `#` symbol to separate the module path from the property name, eg.:
+
+```js
+new WebIDL2JS({
+  importedTypes: {
+    // The `domexception` package exports the wrapper class API
+    // for `DOMException` at the top level of `domexception/webidl-wrapper`:
+    DOMException: "domexception/webidl-wrapper",
+
+    // The `whatwg-url` package exports the wrapper class APIs
+    // for `URL` and `URLSearchParams` as properties of `whatwg-url/webidl-wrapper`:
+    URL: "whatwg-url/webidl-wrapper#URL",
+    URLSearchParams: "whatwg-url/webidl-wrapper#URLSearchParams",
+  }
+});
+```
+
 ## Generated wrapper class file API
 
 The example above showed a simplified generated wrapper file with only three exports: `create`, `is`, and `interface`. In reality the generated wrapper file will contain more functionality, documented here. This functionality is different between generated wrapper files for interfaces and for dictionaries.
@@ -264,6 +287,10 @@ Performs the Web IDL conversion algorithm for this interface, converting _value_
 
 In practice, this means doing a type-check equivalent to `is(value)`, and if it passes, returns the corresponding impl. If the type-check fails, it throws an informative exception. _context_ can be used to describe the provided value in any resulting error message.
 
+#### `validate(value, { context })`
+
+Like `convert(value)`, but returns the wrapper class. This exists to support imported types, which can't use `utils.wrapperFromImpl(value)` as the wrapper and impl private symbols aren't shared between packages.
+
 #### `install(globalObject, globalNames)`
 
 This method creates a brand new wrapper constructor and prototype and attach it to the passed `globalObject`. It also registers the created constructor with the `globalObject`'s global constructor registry, which makes `create()`, `createImpl()`, and `setup()` work. (Thus, it is important to invoke `install()` before invoking those methods, as otherwise they will throw.)
diff --git a/lib/constructs/interface.js b/lib/constructs/interface.js
index 4ae4f19c..11d30825 100644
--- a/lib/constructs/interface.js
+++ b/lib/constructs/interface.js
@@ -605,6 +605,12 @@ class Interface {
       exports.isImpl = value => {
         return utils.isObject(value) && value instanceof Impl.implementation;
       };
+      exports.validate = (value, { context = "The provided value" } = {}) => {
+        if (!exports.is(value)) {
+          throw new TypeError(\`\${context} is not of type '${this.name}'.\`);
+        }
+        return value;
+      };
       exports.convert = (value, { context = "The provided value" } = {}) => {
         if (exports.is(value)) {
           return utils.implForWrapper(value);
diff --git a/lib/context.js b/lib/context.js
index d2bb1dc6..91205b6c 100644
--- a/lib/context.js
+++ b/lib/context.js
@@ -24,8 +24,11 @@ class Context {
     processCEReactions = defaultProcessor,
     processHTMLConstructor = defaultProcessor,
     processReflect = null,
-    options = { suppressErrors: false }
-  } = {}) {
+    importedTypes = {},
+    options = {
+      suppressErrors: false
+    }
+  }) {
     this.implSuffix = implSuffix;
     this.processCEReactions = processCEReactions;
     this.processHTMLConstructor = processHTMLConstructor;
@@ -33,6 +36,12 @@ class Context {
     this.options = options;
 
     this.initialize();
+    this.importedTypes = new Map(
+      Object.entries(importedTypes).map(([name, data]) => {
+        const [path, property] = data.split("#", 2);
+        return [name, { path, property }];
+      })
+    );
   }
 
   initialize() {
@@ -75,6 +84,9 @@ class Context {
     if (this.enumerations.has(name)) {
       return "enumeration";
     }
+    if (this.importedTypes.has(name)) {
+      return "webidl2js:imported";
+    }
     return undefined;
   }
 
diff --git a/lib/transformer.js b/lib/transformer.js
index 969f544f..f188d618 100644
--- a/lib/transformer.js
+++ b/lib/transformer.js
@@ -22,6 +22,9 @@ class Transformer {
       processCEReactions: opts.processCEReactions,
       processHTMLConstructor: opts.processHTMLConstructor,
       processReflect: opts.processReflect,
+      importedTypes: {
+        ...opts.importedTypes
+      },
       options: {
         suppressErrors: Boolean(opts.suppressErrors)
       }
diff --git a/lib/types.js b/lib/types.js
index 3ec2d5f0..8f4d03c7 100644
--- a/lib/types.js
+++ b/lib/types.js
@@ -26,7 +26,14 @@ function mergeExtAttrs(a = [], b = []) {
 }
 
 // Types of types that generate an output file.
-const resolvedTypes = new Set(["callback", "callback interface", "dictionary", "enumeration", "interface"]);
+const resolvedTypes = new Set([
+  "callback",
+  "callback interface",
+  "dictionary",
+  "enumeration",
+  "interface",
+  "webidl2js:imported"
+]);
 
 function resolveType(ctx, idlType, stack = []) {
   if (resolvedMap.has(idlType)) {
@@ -107,6 +114,7 @@ function generateTypeConversion(ctx, name, idlType, argAttrs = [], parentName, e
     }
   }
 
+  let typeKind;
   if (idlType.union) {
     // union type
     generateUnion();
@@ -130,13 +138,20 @@ function generateTypeConversion(ctx, name, idlType, argAttrs = [], parentName, e
   ) {
     // string or number type compatible with webidl-conversions
     generateGeneric(`conversions["${idlType.idlType}"]`);
-  } else if (resolvedTypes.has(ctx.typeOf(idlType.idlType))) {
+  } else if (resolvedTypes.has(typeKind = ctx.typeOf(idlType.idlType))) {
     // callback functions, callback interfaces, dictionaries, enumerations, and interfaces
     let fn;
     // Avoid requiring the interface itself
     if (idlType.idlType !== parentName) {
-      fn = `${idlType.idlType}.convert`;
-      requires.addRelative(idlType.idlType);
+      // webidl2js:imported types can't use `convert`, as we'd have no way
+      // to convert them back to their wrappers.
+      if (typeKind === "webidl2js:imported") {
+        const { path, property } = ctx.importedTypes.get(idlType.idlType);
+        fn = `${requires.add(path, property)}.validate`;
+      } else {
+        fn = `${idlType.idlType}.convert`;
+        requires.addRelative(idlType.idlType);
+      }
     } else {
       fn = `exports.convert`;
     }
diff --git a/lib/utils.js b/lib/utils.js
index 004d78bd..54bf5271 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -104,7 +104,7 @@ function formatArgs(args) {
 }
 
 function toKey(type, func = "") {
-  return String(func + type).replace(/[./-]+/g, " ").trim().replace(/ /g, "_");
+  return String(`${func}@${type}`).replace(/[@./-]+/g, " ").trim().replace(/ /g, "_");
 }
 
 const PACKAGE_NAME_REGEX = /^(?:@([^/]+?)[/])?([^/]+?)$/u;
diff --git a/test/__snapshots__/test.js.snap b/test/__snapshots__/test.js.snap
index 8023678b..116581d1 100644
--- a/test/__snapshots__/test.js.snap
+++ b/test/__snapshots__/test.js.snap
@@ -84,6 +84,292 @@ exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
 "
 `;
 
+exports[`with external imports UsingExternal.webidl 1`] = `
+"\\"use strict\\";
+
+const conversions = require(\\"webidl-conversions\\");
+const utils = require(\\"./utils.js\\");
+
+const domexception_webidl2js_wrapper = require(\\"domexception/webidl2js-wrapper.js\\");
+const URL_whatwg_url_webidl2js_wrapper = require(\\"whatwg-url/webidl2js-wrapper.js\\").URL;
+const URLSearchParams_whatwg_url_webidl2js_wrapper = require(\\"whatwg-url/webidl2js-wrapper.js\\").URLSearchParams;
+const implSymbol = utils.implSymbol;
+const ctorRegistrySymbol = utils.ctorRegistrySymbol;
+
+const interfaceName = \\"UsingExternal\\";
+
+exports.is = value => {
+  return utils.isObject(value) && utils.hasOwn(value, implSymbol) && value[implSymbol] instanceof Impl.implementation;
+};
+exports.isImpl = value => {
+  return utils.isObject(value) && value instanceof Impl.implementation;
+};
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'UsingExternal'.\`);
+  }
+  return value;
+};
+exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
+  if (exports.is(value)) {
+    return utils.implForWrapper(value);
+  }
+  throw new TypeError(\`\${context} is not of type 'UsingExternal'.\`);
+};
+
+function makeWrapper(globalObject) {
+  if (globalObject[ctorRegistrySymbol] === undefined) {
+    throw new Error(\\"Internal error: invalid global object\\");
+  }
+
+  const ctor = globalObject[ctorRegistrySymbol][\\"UsingExternal\\"];
+  if (ctor === undefined) {
+    throw new Error(\\"Internal error: constructor UsingExternal is not installed on the passed global object\\");
+  }
+
+  return Object.create(ctor.prototype);
+}
+
+exports.create = (globalObject, constructorArgs, privateData) => {
+  const wrapper = makeWrapper(globalObject);
+  return exports.setup(wrapper, globalObject, constructorArgs, privateData);
+};
+
+exports.createImpl = (globalObject, constructorArgs, privateData) => {
+  const wrapper = exports.create(globalObject, constructorArgs, privateData);
+  return utils.implForWrapper(wrapper);
+};
+
+exports._internalSetup = (wrapper, globalObject) => {};
+
+exports.setup = (wrapper, globalObject, constructorArgs = [], privateData = {}) => {
+  privateData.wrapper = wrapper;
+
+  exports._internalSetup(wrapper, globalObject);
+  Object.defineProperty(wrapper, implSymbol, {
+    value: new Impl.implementation(globalObject, constructorArgs, privateData),
+    configurable: true
+  });
+
+  wrapper[implSymbol][utils.wrapperSymbol] = wrapper;
+  if (Impl.init) {
+    Impl.init(wrapper[implSymbol]);
+  }
+  return wrapper;
+};
+
+exports.new = globalObject => {
+  const wrapper = makeWrapper(globalObject);
+
+  exports._internalSetup(wrapper, globalObject);
+  Object.defineProperty(wrapper, implSymbol, {
+    value: Object.create(Impl.implementation.prototype),
+    configurable: true
+  });
+
+  wrapper[implSymbol][utils.wrapperSymbol] = wrapper;
+  if (Impl.init) {
+    Impl.init(wrapper[implSymbol]);
+  }
+  return wrapper[implSymbol];
+};
+
+const exposed = new Set([\\"Window\\"]);
+
+exports.install = (globalObject, globalNames) => {
+  if (!globalNames.some(globalName => exposed.has(globalName))) {
+    return;
+  }
+  class UsingExternal {
+    constructor() {
+      throw new TypeError(\\"Illegal constructor\\");
+    }
+
+    methodImportedDOMException(domException) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'methodImportedDOMException' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      if (arguments.length < 1) {
+        throw new TypeError(
+          \\"Failed to execute 'methodImportedDOMException' on 'UsingExternal': 1 argument required, but only \\" +
+            arguments.length +
+            \\" present.\\"
+        );
+      }
+      const args = [];
+      {
+        let curArg = arguments[0];
+        curArg = domexception_webidl2js_wrapper.validate(curArg, {
+          context: \\"Failed to execute 'methodImportedDOMException' on 'UsingExternal': parameter 1\\"
+        });
+        args.push(curArg);
+      }
+      return esValue[implSymbol].methodImportedDOMException(...args);
+    }
+
+    methodImportedURL(url) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+      if (!exports.is(esValue)) {
+        throw new TypeError(\\"'methodImportedURL' called on an object that is not a valid instance of UsingExternal.\\");
+      }
+
+      if (arguments.length < 1) {
+        throw new TypeError(
+          \\"Failed to execute 'methodImportedURL' on 'UsingExternal': 1 argument required, but only \\" +
+            arguments.length +
+            \\" present.\\"
+        );
+      }
+      const args = [];
+      {
+        let curArg = arguments[0];
+        curArg = URL_whatwg_url_webidl2js_wrapper.validate(curArg, {
+          context: \\"Failed to execute 'methodImportedURL' on 'UsingExternal': parameter 1\\"
+        });
+        args.push(curArg);
+      }
+      return esValue[implSymbol].methodImportedURL(...args);
+    }
+
+    methodImportedURLSearchParams(url) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'methodImportedURLSearchParams' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      if (arguments.length < 1) {
+        throw new TypeError(
+          \\"Failed to execute 'methodImportedURLSearchParams' on 'UsingExternal': 1 argument required, but only \\" +
+            arguments.length +
+            \\" present.\\"
+        );
+      }
+      const args = [];
+      {
+        let curArg = arguments[0];
+        curArg = URLSearchParams_whatwg_url_webidl2js_wrapper.validate(curArg, {
+          context: \\"Failed to execute 'methodImportedURLSearchParams' on 'UsingExternal': parameter 1\\"
+        });
+        args.push(curArg);
+      }
+      return esValue[implSymbol].methodImportedURLSearchParams(...args);
+    }
+
+    get propertyImportedDOMException() {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'get propertyImportedDOMException' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      return utils.tryWrapperForImpl(esValue[implSymbol][\\"propertyImportedDOMException\\"]);
+    }
+
+    set propertyImportedDOMException(V) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'set propertyImportedDOMException' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      V = domexception_webidl2js_wrapper.validate(V, {
+        context: \\"Failed to set the 'propertyImportedDOMException' property on 'UsingExternal': The provided value\\"
+      });
+
+      esValue[implSymbol][\\"propertyImportedDOMException\\"] = V;
+    }
+
+    get propertyImportedURL() {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'get propertyImportedURL' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      return utils.tryWrapperForImpl(esValue[implSymbol][\\"propertyImportedURL\\"]);
+    }
+
+    set propertyImportedURL(V) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'set propertyImportedURL' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      V = URL_whatwg_url_webidl2js_wrapper.validate(V, {
+        context: \\"Failed to set the 'propertyImportedURL' property on 'UsingExternal': The provided value\\"
+      });
+
+      esValue[implSymbol][\\"propertyImportedURL\\"] = V;
+    }
+
+    get propertyImportedURLSearchParams() {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'get propertyImportedURLSearchParams' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      return utils.tryWrapperForImpl(esValue[implSymbol][\\"propertyImportedURLSearchParams\\"]);
+    }
+
+    set propertyImportedURLSearchParams(V) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'set propertyImportedURLSearchParams' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      V = URLSearchParams_whatwg_url_webidl2js_wrapper.validate(V, {
+        context: \\"Failed to set the 'propertyImportedURLSearchParams' property on 'UsingExternal': The provided value\\"
+      });
+
+      esValue[implSymbol][\\"propertyImportedURLSearchParams\\"] = V;
+    }
+  }
+  Object.defineProperties(UsingExternal.prototype, {
+    methodImportedDOMException: { enumerable: true },
+    methodImportedURL: { enumerable: true },
+    methodImportedURLSearchParams: { enumerable: true },
+    propertyImportedDOMException: { enumerable: true },
+    propertyImportedURL: { enumerable: true },
+    propertyImportedURLSearchParams: { enumerable: true },
+    [Symbol.toStringTag]: { value: \\"UsingExternal\\", configurable: true }
+  });
+  if (globalObject[ctorRegistrySymbol] === undefined) {
+    globalObject[ctorRegistrySymbol] = Object.create(null);
+  }
+  globalObject[ctorRegistrySymbol][interfaceName] = UsingExternal;
+
+  Object.defineProperty(globalObject, interfaceName, {
+    configurable: true,
+    writable: true,
+    value: UsingExternal
+  });
+};
+
+const Impl = require(\\"../implementations/UsingExternal.js\\");
+"
+`;
+
 exports[`with processors AsyncCallbackFunction.webidl 1`] = `
 "\\"use strict\\";
 
@@ -234,6 +520,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'AsyncIterablePairArgs'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -507,6 +799,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'AsyncIterablePairNoArgs'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -718,6 +1016,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'AsyncIterableValueArgs'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -906,6 +1210,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'AsyncIterableValueNoArgs'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -1110,6 +1420,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'AsyncIterableWithReturn'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -1250,6 +1566,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'BufferSourceTypes'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -1525,6 +1847,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'CEReactions'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -2020,6 +2348,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'DOMImplementation'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -2254,6 +2588,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'DOMRect'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -2608,6 +2948,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'DictionaryConvert'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -2744,6 +3090,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Enum'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -2942,6 +3294,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'EventTarget'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -3089,6 +3447,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Global'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -3319,6 +3683,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'HTMLConstructor'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -3430,6 +3800,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'LegacyLenientAttributes'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -3635,6 +4011,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'LegacyUnforgeable'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -3844,6 +4226,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'LegacyUnforgeableMap'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -4153,6 +4541,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'MixedIn'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -4419,6 +4813,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Overloads'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -4840,6 +5240,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'PromiseTypes'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -5091,6 +5497,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Reflect'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -5391,6 +5803,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Replaceable'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -5562,6 +5980,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'SeqAndRec'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -5878,6 +6302,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Static'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -6041,6 +6471,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Storage'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -6434,6 +6870,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'StringifierAttribute'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -6566,6 +7008,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'StringifierDefaultOperation'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -6691,6 +7139,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'StringifierNamedOperation'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -6828,6 +7282,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'StringifierOperation'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -6951,6 +7411,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'TypedefsAndUnions'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -7509,6 +7975,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'URL'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -8022,6 +8494,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'URLList'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -8367,6 +8845,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'URLSearchParams'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -8798,6 +9282,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'URLSearchParamsCollection'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -9168,6 +9658,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'URLSearchParamsCollection2'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -9509,6 +10005,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'UnderscoredProperties'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -9711,6 +10213,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Unscopable'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -9859,6 +10367,277 @@ const Impl = require(\\"../implementations/Unscopable.js\\");
 "
 `;
 
+exports[`with processors UsingExternal.webidl 1`] = `
+"\\"use strict\\";
+
+const conversions = require(\\"webidl-conversions\\");
+const utils = require(\\"./utils.js\\");
+
+const implSymbol = utils.implSymbol;
+const ctorRegistrySymbol = utils.ctorRegistrySymbol;
+
+const interfaceName = \\"UsingExternal\\";
+
+exports.is = value => {
+  return utils.isObject(value) && utils.hasOwn(value, implSymbol) && value[implSymbol] instanceof Impl.implementation;
+};
+exports.isImpl = value => {
+  return utils.isObject(value) && value instanceof Impl.implementation;
+};
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'UsingExternal'.\`);
+  }
+  return value;
+};
+exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
+  if (exports.is(value)) {
+    return utils.implForWrapper(value);
+  }
+  throw new TypeError(\`\${context} is not of type 'UsingExternal'.\`);
+};
+
+function makeWrapper(globalObject) {
+  if (globalObject[ctorRegistrySymbol] === undefined) {
+    throw new Error(\\"Internal error: invalid global object\\");
+  }
+
+  const ctor = globalObject[ctorRegistrySymbol][\\"UsingExternal\\"];
+  if (ctor === undefined) {
+    throw new Error(\\"Internal error: constructor UsingExternal is not installed on the passed global object\\");
+  }
+
+  return Object.create(ctor.prototype);
+}
+
+exports.create = (globalObject, constructorArgs, privateData) => {
+  const wrapper = makeWrapper(globalObject);
+  return exports.setup(wrapper, globalObject, constructorArgs, privateData);
+};
+
+exports.createImpl = (globalObject, constructorArgs, privateData) => {
+  const wrapper = exports.create(globalObject, constructorArgs, privateData);
+  return utils.implForWrapper(wrapper);
+};
+
+exports._internalSetup = (wrapper, globalObject) => {};
+
+exports.setup = (wrapper, globalObject, constructorArgs = [], privateData = {}) => {
+  privateData.wrapper = wrapper;
+
+  exports._internalSetup(wrapper, globalObject);
+  Object.defineProperty(wrapper, implSymbol, {
+    value: new Impl.implementation(globalObject, constructorArgs, privateData),
+    configurable: true
+  });
+
+  wrapper[implSymbol][utils.wrapperSymbol] = wrapper;
+  if (Impl.init) {
+    Impl.init(wrapper[implSymbol]);
+  }
+  return wrapper;
+};
+
+exports.new = globalObject => {
+  const wrapper = makeWrapper(globalObject);
+
+  exports._internalSetup(wrapper, globalObject);
+  Object.defineProperty(wrapper, implSymbol, {
+    value: Object.create(Impl.implementation.prototype),
+    configurable: true
+  });
+
+  wrapper[implSymbol][utils.wrapperSymbol] = wrapper;
+  if (Impl.init) {
+    Impl.init(wrapper[implSymbol]);
+  }
+  return wrapper[implSymbol];
+};
+
+const exposed = new Set([\\"Window\\"]);
+
+exports.install = (globalObject, globalNames) => {
+  if (!globalNames.some(globalName => exposed.has(globalName))) {
+    return;
+  }
+  class UsingExternal {
+    constructor() {
+      throw new TypeError(\\"Illegal constructor\\");
+    }
+
+    methodImportedDOMException(domException) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'methodImportedDOMException' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      if (arguments.length < 1) {
+        throw new TypeError(
+          \\"Failed to execute 'methodImportedDOMException' on 'UsingExternal': 1 argument required, but only \\" +
+            arguments.length +
+            \\" present.\\"
+        );
+      }
+      const args = [];
+      {
+        let curArg = arguments[0];
+        curArg = utils.tryImplForWrapper(curArg);
+        args.push(curArg);
+      }
+      return esValue[implSymbol].methodImportedDOMException(...args);
+    }
+
+    methodImportedURL(url) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+      if (!exports.is(esValue)) {
+        throw new TypeError(\\"'methodImportedURL' called on an object that is not a valid instance of UsingExternal.\\");
+      }
+
+      if (arguments.length < 1) {
+        throw new TypeError(
+          \\"Failed to execute 'methodImportedURL' on 'UsingExternal': 1 argument required, but only \\" +
+            arguments.length +
+            \\" present.\\"
+        );
+      }
+      const args = [];
+      {
+        let curArg = arguments[0];
+        curArg = utils.tryImplForWrapper(curArg);
+        args.push(curArg);
+      }
+      return esValue[implSymbol].methodImportedURL(...args);
+    }
+
+    methodImportedURLSearchParams(url) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'methodImportedURLSearchParams' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      if (arguments.length < 1) {
+        throw new TypeError(
+          \\"Failed to execute 'methodImportedURLSearchParams' on 'UsingExternal': 1 argument required, but only \\" +
+            arguments.length +
+            \\" present.\\"
+        );
+      }
+      const args = [];
+      {
+        let curArg = arguments[0];
+        curArg = utils.tryImplForWrapper(curArg);
+        args.push(curArg);
+      }
+      return esValue[implSymbol].methodImportedURLSearchParams(...args);
+    }
+
+    get propertyImportedDOMException() {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'get propertyImportedDOMException' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      return utils.tryWrapperForImpl(esValue[implSymbol][\\"propertyImportedDOMException\\"]);
+    }
+
+    set propertyImportedDOMException(V) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'set propertyImportedDOMException' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      V = utils.tryImplForWrapper(V);
+
+      esValue[implSymbol][\\"propertyImportedDOMException\\"] = V;
+    }
+
+    get propertyImportedURL() {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'get propertyImportedURL' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      return utils.tryWrapperForImpl(esValue[implSymbol][\\"propertyImportedURL\\"]);
+    }
+
+    set propertyImportedURL(V) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'set propertyImportedURL' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      V = utils.tryImplForWrapper(V);
+
+      esValue[implSymbol][\\"propertyImportedURL\\"] = V;
+    }
+
+    get propertyImportedURLSearchParams() {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'get propertyImportedURLSearchParams' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      return utils.tryWrapperForImpl(esValue[implSymbol][\\"propertyImportedURLSearchParams\\"]);
+    }
+
+    set propertyImportedURLSearchParams(V) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'set propertyImportedURLSearchParams' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      V = utils.tryImplForWrapper(V);
+
+      esValue[implSymbol][\\"propertyImportedURLSearchParams\\"] = V;
+    }
+  }
+  Object.defineProperties(UsingExternal.prototype, {
+    methodImportedDOMException: { enumerable: true },
+    methodImportedURL: { enumerable: true },
+    methodImportedURLSearchParams: { enumerable: true },
+    propertyImportedDOMException: { enumerable: true },
+    propertyImportedURL: { enumerable: true },
+    propertyImportedURLSearchParams: { enumerable: true },
+    [Symbol.toStringTag]: { value: \\"UsingExternal\\", configurable: true }
+  });
+  if (globalObject[ctorRegistrySymbol] === undefined) {
+    globalObject[ctorRegistrySymbol] = Object.create(null);
+  }
+  globalObject[ctorRegistrySymbol][interfaceName] = UsingExternal;
+
+  Object.defineProperty(globalObject, interfaceName, {
+    configurable: true,
+    writable: true,
+    value: UsingExternal
+  });
+};
+
+const Impl = require(\\"../implementations/UsingExternal.js\\");
+"
+`;
+
 exports[`with processors Variadic.webidl 1`] = `
 "\\"use strict\\";
 
@@ -9877,6 +10656,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Variadic'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -10143,6 +10928,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'ZeroArgConstructor'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -10387,6 +11178,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'AsyncIterablePairArgs'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -10660,6 +11457,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'AsyncIterablePairNoArgs'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -10871,6 +11674,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'AsyncIterableValueArgs'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -11059,6 +11868,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'AsyncIterableValueNoArgs'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -11263,6 +12078,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'AsyncIterableWithReturn'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -11403,6 +12224,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'BufferSourceTypes'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -11677,6 +12504,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'CEReactions'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -12132,6 +12965,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'DOMImplementation'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -12366,6 +13205,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'DOMRect'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -12720,6 +13565,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'DictionaryConvert'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -12856,6 +13707,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Enum'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -13054,6 +13911,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'EventTarget'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -13201,6 +14064,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Global'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -13430,6 +14299,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'HTMLConstructor'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -13541,6 +14416,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'LegacyLenientAttributes'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -13746,6 +14627,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'LegacyUnforgeable'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -13955,6 +14842,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'LegacyUnforgeableMap'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -14264,6 +15157,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'MixedIn'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -14530,6 +15429,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Overloads'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -14951,6 +15856,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'PromiseTypes'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -15201,6 +16112,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Reflect'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -15487,6 +16404,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Replaceable'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -15658,6 +16581,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'SeqAndRec'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -15974,6 +16903,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Static'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -16137,6 +17072,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Storage'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -16530,6 +17471,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'StringifierAttribute'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -16662,6 +17609,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'StringifierDefaultOperation'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -16787,6 +17740,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'StringifierNamedOperation'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -16924,6 +17883,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'StringifierOperation'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -17047,6 +18012,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'TypedefsAndUnions'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -17605,6 +18576,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'URL'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -18118,6 +19095,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'URLList'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -18463,6 +19446,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'URLSearchParams'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -18894,6 +19883,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'URLSearchParamsCollection'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -19264,6 +20259,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'URLSearchParamsCollection2'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -19605,6 +20606,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'UnderscoredProperties'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -19807,6 +20814,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Unscopable'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -19955,6 +20968,277 @@ const Impl = require(\\"../implementations/Unscopable.js\\");
 "
 `;
 
+exports[`without processors UsingExternal.webidl 1`] = `
+"\\"use strict\\";
+
+const conversions = require(\\"webidl-conversions\\");
+const utils = require(\\"./utils.js\\");
+
+const implSymbol = utils.implSymbol;
+const ctorRegistrySymbol = utils.ctorRegistrySymbol;
+
+const interfaceName = \\"UsingExternal\\";
+
+exports.is = value => {
+  return utils.isObject(value) && utils.hasOwn(value, implSymbol) && value[implSymbol] instanceof Impl.implementation;
+};
+exports.isImpl = value => {
+  return utils.isObject(value) && value instanceof Impl.implementation;
+};
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'UsingExternal'.\`);
+  }
+  return value;
+};
+exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
+  if (exports.is(value)) {
+    return utils.implForWrapper(value);
+  }
+  throw new TypeError(\`\${context} is not of type 'UsingExternal'.\`);
+};
+
+function makeWrapper(globalObject) {
+  if (globalObject[ctorRegistrySymbol] === undefined) {
+    throw new Error(\\"Internal error: invalid global object\\");
+  }
+
+  const ctor = globalObject[ctorRegistrySymbol][\\"UsingExternal\\"];
+  if (ctor === undefined) {
+    throw new Error(\\"Internal error: constructor UsingExternal is not installed on the passed global object\\");
+  }
+
+  return Object.create(ctor.prototype);
+}
+
+exports.create = (globalObject, constructorArgs, privateData) => {
+  const wrapper = makeWrapper(globalObject);
+  return exports.setup(wrapper, globalObject, constructorArgs, privateData);
+};
+
+exports.createImpl = (globalObject, constructorArgs, privateData) => {
+  const wrapper = exports.create(globalObject, constructorArgs, privateData);
+  return utils.implForWrapper(wrapper);
+};
+
+exports._internalSetup = (wrapper, globalObject) => {};
+
+exports.setup = (wrapper, globalObject, constructorArgs = [], privateData = {}) => {
+  privateData.wrapper = wrapper;
+
+  exports._internalSetup(wrapper, globalObject);
+  Object.defineProperty(wrapper, implSymbol, {
+    value: new Impl.implementation(globalObject, constructorArgs, privateData),
+    configurable: true
+  });
+
+  wrapper[implSymbol][utils.wrapperSymbol] = wrapper;
+  if (Impl.init) {
+    Impl.init(wrapper[implSymbol]);
+  }
+  return wrapper;
+};
+
+exports.new = globalObject => {
+  const wrapper = makeWrapper(globalObject);
+
+  exports._internalSetup(wrapper, globalObject);
+  Object.defineProperty(wrapper, implSymbol, {
+    value: Object.create(Impl.implementation.prototype),
+    configurable: true
+  });
+
+  wrapper[implSymbol][utils.wrapperSymbol] = wrapper;
+  if (Impl.init) {
+    Impl.init(wrapper[implSymbol]);
+  }
+  return wrapper[implSymbol];
+};
+
+const exposed = new Set([\\"Window\\"]);
+
+exports.install = (globalObject, globalNames) => {
+  if (!globalNames.some(globalName => exposed.has(globalName))) {
+    return;
+  }
+  class UsingExternal {
+    constructor() {
+      throw new TypeError(\\"Illegal constructor\\");
+    }
+
+    methodImportedDOMException(domException) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'methodImportedDOMException' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      if (arguments.length < 1) {
+        throw new TypeError(
+          \\"Failed to execute 'methodImportedDOMException' on 'UsingExternal': 1 argument required, but only \\" +
+            arguments.length +
+            \\" present.\\"
+        );
+      }
+      const args = [];
+      {
+        let curArg = arguments[0];
+        curArg = utils.tryImplForWrapper(curArg);
+        args.push(curArg);
+      }
+      return esValue[implSymbol].methodImportedDOMException(...args);
+    }
+
+    methodImportedURL(url) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+      if (!exports.is(esValue)) {
+        throw new TypeError(\\"'methodImportedURL' called on an object that is not a valid instance of UsingExternal.\\");
+      }
+
+      if (arguments.length < 1) {
+        throw new TypeError(
+          \\"Failed to execute 'methodImportedURL' on 'UsingExternal': 1 argument required, but only \\" +
+            arguments.length +
+            \\" present.\\"
+        );
+      }
+      const args = [];
+      {
+        let curArg = arguments[0];
+        curArg = utils.tryImplForWrapper(curArg);
+        args.push(curArg);
+      }
+      return esValue[implSymbol].methodImportedURL(...args);
+    }
+
+    methodImportedURLSearchParams(url) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'methodImportedURLSearchParams' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      if (arguments.length < 1) {
+        throw new TypeError(
+          \\"Failed to execute 'methodImportedURLSearchParams' on 'UsingExternal': 1 argument required, but only \\" +
+            arguments.length +
+            \\" present.\\"
+        );
+      }
+      const args = [];
+      {
+        let curArg = arguments[0];
+        curArg = utils.tryImplForWrapper(curArg);
+        args.push(curArg);
+      }
+      return esValue[implSymbol].methodImportedURLSearchParams(...args);
+    }
+
+    get propertyImportedDOMException() {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'get propertyImportedDOMException' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      return utils.tryWrapperForImpl(esValue[implSymbol][\\"propertyImportedDOMException\\"]);
+    }
+
+    set propertyImportedDOMException(V) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'set propertyImportedDOMException' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      V = utils.tryImplForWrapper(V);
+
+      esValue[implSymbol][\\"propertyImportedDOMException\\"] = V;
+    }
+
+    get propertyImportedURL() {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'get propertyImportedURL' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      return utils.tryWrapperForImpl(esValue[implSymbol][\\"propertyImportedURL\\"]);
+    }
+
+    set propertyImportedURL(V) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'set propertyImportedURL' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      V = utils.tryImplForWrapper(V);
+
+      esValue[implSymbol][\\"propertyImportedURL\\"] = V;
+    }
+
+    get propertyImportedURLSearchParams() {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'get propertyImportedURLSearchParams' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      return utils.tryWrapperForImpl(esValue[implSymbol][\\"propertyImportedURLSearchParams\\"]);
+    }
+
+    set propertyImportedURLSearchParams(V) {
+      const esValue = this !== null && this !== undefined ? this : globalObject;
+
+      if (!exports.is(esValue)) {
+        throw new TypeError(
+          \\"'set propertyImportedURLSearchParams' called on an object that is not a valid instance of UsingExternal.\\"
+        );
+      }
+
+      V = utils.tryImplForWrapper(V);
+
+      esValue[implSymbol][\\"propertyImportedURLSearchParams\\"] = V;
+    }
+  }
+  Object.defineProperties(UsingExternal.prototype, {
+    methodImportedDOMException: { enumerable: true },
+    methodImportedURL: { enumerable: true },
+    methodImportedURLSearchParams: { enumerable: true },
+    propertyImportedDOMException: { enumerable: true },
+    propertyImportedURL: { enumerable: true },
+    propertyImportedURLSearchParams: { enumerable: true },
+    [Symbol.toStringTag]: { value: \\"UsingExternal\\", configurable: true }
+  });
+  if (globalObject[ctorRegistrySymbol] === undefined) {
+    globalObject[ctorRegistrySymbol] = Object.create(null);
+  }
+  globalObject[ctorRegistrySymbol][interfaceName] = UsingExternal;
+
+  Object.defineProperty(globalObject, interfaceName, {
+    configurable: true,
+    writable: true,
+    value: UsingExternal
+  });
+};
+
+const Impl = require(\\"../implementations/UsingExternal.js\\");
+"
+`;
+
 exports[`without processors Variadic.webidl 1`] = `
 "\\"use strict\\";
 
@@ -19973,6 +21257,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'Variadic'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
@@ -20239,6 +21529,12 @@ exports.is = value => {
 exports.isImpl = value => {
   return utils.isObject(value) && value instanceof Impl.implementation;
 };
+exports.validate = (value, { context = \\"The provided value\\" } = {}) => {
+  if (!exports.is(value)) {
+    throw new TypeError(\`\${context} is not of type 'ZeroArgConstructor'.\`);
+  }
+  return value;
+};
 exports.convert = (value, { context = \\"The provided value\\" } = {}) => {
   if (exports.is(value)) {
     return utils.implForWrapper(value);
diff --git a/test/cases/UsingExternal.webidl b/test/cases/UsingExternal.webidl
new file mode 100644
index 00000000..075e8c22
--- /dev/null
+++ b/test/cases/UsingExternal.webidl
@@ -0,0 +1,10 @@
+[Exposed=Window]
+interface UsingExternal {
+  void methodImportedDOMException(Imported-DOMException domException);
+  void methodImportedURL(Imported-URL url);
+  void methodImportedURLSearchParams(Imported-URLSearchParams url);
+
+  attribute Imported-DOMException propertyImportedDOMException;
+  attribute Imported-URL propertyImportedURL;
+  attribute Imported-URLSearchParams propertyImportedURLSearchParams;
+};
diff --git a/test/test.js b/test/test.js
index a1e045d7..1e950e7b 100644
--- a/test/test.js
+++ b/test/test.js
@@ -118,6 +118,28 @@ describe("with processors", () => {
   }
 });
 
+describe("with external imports", () => {
+  beforeAll(() => {
+    const transformer = new Transformer({
+      importedTypes: {
+        "Imported-DOMException": "domexception/webidl2js-wrapper",
+        "Imported-URL": "whatwg-url/webidl2js-wrapper#URL",
+        "Imported-URLSearchParams": "whatwg-url/webidl2js-wrapper#URLSearchParams"
+      }
+    });
+    transformer.addSource(casesDir, implsDir);
+
+    return transformer.generate(outputDir);
+  });
+
+  test("UsingExternal.webidl", () => {
+    const outputFile = path.resolve(outputDir, "UsingExternal.js");
+    const output = fs.readFileSync(outputFile, { encoding: "utf-8" });
+
+    expect(output).toMatchSnapshot();
+  });
+});
+
 test("utils.js", () => {
   const input = fs.readFileSync(path.resolve(rootDir, "lib/output/utils.js"), { encoding: "utf-8" });
   const output = fs.readFileSync(path.resolve(outputDir, "utils.js"), { encoding: "utf-8" });