diff --git a/docs/api.md b/docs/api.md
index 7431627b6d550..4cdbd3dd6c72a 100644
--- a/docs/api.md
+++ b/docs/api.md
@@ -71,7 +71,7 @@ This object can be used to launch or connect to Chromium, returning instances of
 #### playwright.devices
 - returns: <[Object]>
 
-Returns a list of devices to be used with [`browser.newContext(options)`](#browsernewcontextoptions) or [`browser.newPage(options)`](#browsernewpageoptions). Actual list of devices can be found in [src/deviceDescriptors.ts](https://github.com/Microsoft/playwright/blob/master/src/deviceDescriptors.ts).
+Returns a list of devices to be used with [`browser.newContext([options])`](#browsernewcontextoptions) or [`browser.newPage([options])`](#browsernewpageoptions). Actual list of devices can be found in [src/deviceDescriptors.ts](https://github.com/Microsoft/playwright/blob/master/src/deviceDescriptors.ts).
 
 ```js
 const { webkit, devices } = require('playwright');
@@ -145,14 +145,14 @@ const { firefox } = require('playwright');  // Or 'chromium' or 'webkit'.
 })();
 ```
 
-See [ChromiumBrowser], [FirefoxBrowser] and [WebKitBrowser] for browser-specific features. Note that [browserType.connect(options)](#browsertypeconnectoptions) and [browserType.launch(options)](#browsertypelaunchoptions) always return a specific browser instance, based on the browser being connected to or launched.
+See [ChromiumBrowser], [FirefoxBrowser] and [WebKitBrowser] for browser-specific features. Note that [browserType.connect(options)](#browsertypeconnectoptions) and [browserType.launch([options])](#browsertypelaunchoptions) always return a specific browser instance, based on the browser being connected to or launched.
 
 <!-- GEN:toc -->
 - [event: 'disconnected'](#event-disconnected)
 - [browser.close()](#browserclose)
 - [browser.contexts()](#browsercontexts)
 - [browser.isConnected()](#browserisconnected)
-- [browser.newContext(options)](#browsernewcontextoptions)
+- [browser.newContext([options])](#browsernewcontextoptions)
 - [browser.newPage([options])](#browsernewpageoptions)
 <!-- GEN:stop -->
 
@@ -182,7 +182,7 @@ a single instance of [BrowserContext].
 
 Indicates that the browser is connected.
 
-#### browser.newContext(options)
+#### browser.newContext([options])
 - `options` <[Object]>
   - `ignoreHTTPSErrors` <?[boolean]> Whether to ignore HTTPS errors during navigation. Defaults to `false`.
   - `bypassCSP` <?[boolean]> Toggles bypassing page's Content-Security-Policy.
@@ -604,8 +604,8 @@ page.removeListener('request', logRequest);
 - [page.evaluate(pageFunction[, ...args])](#pageevaluatepagefunction-args)
 - [page.evaluateHandle(pageFunction[, ...args])](#pageevaluatehandlepagefunction-args)
 - [page.exposeFunction(name, playwrightFunction)](#pageexposefunctionname-playwrightfunction)
-- [page.fill(selector, value, options)](#pagefillselector-value-options)
-- [page.focus(selector, options)](#pagefocusselector-options)
+- [page.fill(selector, value[, options])](#pagefillselector-value-options)
+- [page.focus(selector[, options])](#pagefocusselector-options)
 - [page.frames()](#pageframes)
 - [page.goBack([options])](#pagegobackoptions)
 - [page.goForward([options])](#pagegoforwardoptions)
@@ -620,7 +620,7 @@ page.removeListener('request', logRequest);
 - [page.reload([options])](#pagereloadoptions)
 - [page.route(url, handler)](#pagerouteurl-handler)
 - [page.screenshot([options])](#pagescreenshotoptions)
-- [page.select(selector, value, options)](#pageselectselector-value-options)
+- [page.select(selector, value[, options])](#pageselectselector-value-options)
 - [page.setCacheEnabled([enabled])](#pagesetcacheenabledenabled)
 - [page.setContent(html[, options])](#pagesetcontenthtml-options)
 - [page.setDefaultNavigationTimeout(timeout)](#pagesetdefaultnavigationtimeouttimeout)
@@ -1135,7 +1135,7 @@ const fs = require('fs');
 })();
 ```
 
-#### page.fill(selector, value, options)
+#### page.fill(selector, value[, options])
 - `selector` <[string]> A selector to query page for.
 - `value` <[string]> Value to fill for the `<input>`, `<textarea>` or `[contenteditable]` element.
 - `options` <[Object]>
@@ -1150,7 +1150,7 @@ If there's no text `<input>`, `<textarea>` or `[contenteditable]` element matchi
 
 Shortcut for [page.mainFrame().fill()](#framefillselector-value)
 
-#### page.focus(selector, options)
+#### page.focus(selector[, options])
 - `selector` <[string]> A selector of an element to focus. If there are multiple elements satisfying the selector, the first will be focused.
 - `options` <[Object]>
   - `waitFor` <[boolean]> Whether to wait for the element to be present in the dom. Defaults to `true`.
@@ -1216,7 +1216,7 @@ Navigate to the next page in history.
 
 > **NOTE** Headless mode doesn't support navigation to a PDF document. See the [upstream issue](https://bugs.chromium.org/p/chromium/issues/detail?id=761295).
 
-Shortcut for [page.mainFrame().goto(url, options)](#framegotourl-options)
+Shortcut for [page.mainFrame().goto(url[, options])](#framegotourl-options)
 
 #### page.hover(selector[, options])
 - `selector` <[string]> A selector to search for element to hover. If there are multiple elements satisfying the selector, the first will be hovered.
@@ -1381,7 +1381,7 @@ await browser.close();
 
 > **NOTE** Screenshots take at least 1/6 second on Chromium OS X and Chromium Windows. See https://crbug.com/741689 for discussion.
 
-#### page.select(selector, value, options)
+#### page.select(selector, value[, options])
 - `selector` <[string]> A selector to query frame for.
 - `value` <[string]|[ElementHandle]|[Object]|[Array]<[string]>|[Array]<[ElementHandle]>|[Array]<[Object]>> Options to select. If the `<select>` has the `multiple` attribute, all matching options are selected, otherwise only the first option matching one of the passed options is selected. String values are equivalent to `{value:'string'}`. Option is considered matching if all specified properties match.
   - `value` <[string]> Matches by `option.value`.
@@ -1412,7 +1412,7 @@ page.select('select#colors', { value: 'blue' }, { index: 2 }, 'red');
 Shortcut for [page.mainFrame().select()](#frameselectselector-values)
 
 #### page.setCacheEnabled([enabled])
-- `enabled` <[boolean]> sets the `enabled` state of the cache.
+- `enabled` <[boolean]> sets the `enabled` state of the cache. Defaults to `true`.
 - returns: <[Promise]>
 
 Toggles ignoring cache for each request based on the enabled state. By default, caching is enabled.
@@ -1468,7 +1468,7 @@ The extra HTTP headers will be sent with every request the page initiates.
   - `height` <[number]> page height in pixels. **required**
 - returns: <[Promise]>
 
-In the case of multiple pages in a single browser, each page can have its own viewport size. However, [browser.newContext(options)](#browsernewcontextoptions) allows to set viewport size (and more) for all pages in the context at once.
+In the case of multiple pages in a single browser, each page can have its own viewport size. However, [browser.newContext([options])](#browsernewcontextoptions) allows to set viewport size (and more) for all pages in the context at once.
 
 `page.setViewportSize` will resize the page. A lot of websites don't expect phones to change size, so you should set the viewport size before navigating to the page.
 
@@ -1800,15 +1800,15 @@ An example of getting text from an iframe element:
 - [frame.dblclick(selector[, options])](#framedblclickselector-options)
 - [frame.evaluate(pageFunction[, ...args])](#frameevaluatepagefunction-args)
 - [frame.evaluateHandle(pageFunction[, ...args])](#frameevaluatehandlepagefunction-args)
-- [frame.fill(selector, value, options)](#framefillselector-value-options)
-- [frame.focus(selector, options)](#framefocusselector-options)
+- [frame.fill(selector, value[, options])](#framefillselector-value-options)
+- [frame.focus(selector[, options])](#framefocusselector-options)
 - [frame.frameElement()](#frameframeelement)
 - [frame.goto(url[, options])](#framegotourl-options)
 - [frame.hover(selector[, options])](#framehoverselector-options)
 - [frame.isDetached()](#frameisdetached)
 - [frame.name()](#framename)
 - [frame.parentFrame()](#frameparentframe)
-- [frame.select(selector, value, options)](#frameselectselector-value-options)
+- [frame.select(selector, value[, options])](#frameselectselector-value-options)
 - [frame.setContent(html[, options])](#framesetcontenthtml-options)
 - [frame.title()](#frametitle)
 - [frame.tripleclick(selector[, options])](#frametripleclickselector-options)
@@ -2025,7 +2025,7 @@ console.log(await resultHandle.jsonValue());
 await resultHandle.dispose();
 ```
 
-#### frame.fill(selector, value, options)
+#### frame.fill(selector, value[, options])
 - `selector` <[string]> A selector to query page for.
 - `value` <[string]> Value to fill for the `<input>`, `<textarea>` or `[contenteditable]` element.
 - `options` <[Object]>
@@ -2036,7 +2036,7 @@ await resultHandle.dispose();
 This method focuses the element and triggers an `input` event after filling.
 If there's no text `<input>`, `<textarea>` or `[contenteditable]` element matching `selector`, the method throws an error.
 
-#### frame.focus(selector, options)
+#### frame.focus(selector[, options])
 - `selector` <[string]> A selector of an element to focus. If there are multiple elements satisfying the selector, the first will be focused.
 - `options` <[Object]>
   - `waitFor` <[boolean]> Whether to wait for the element to be present in the dom. Defaults to `true`.
@@ -2116,7 +2116,7 @@ If the name is empty, returns the id attribute instead.
 #### frame.parentFrame()
 - returns: <?[Frame]> Parent frame, if any. Detached frames and main frames return `null`.
 
-#### frame.select(selector, value, options)
+#### frame.select(selector, value[, options])
 - `selector` <[string]> A selector to query frame for.
 - `value` <[string]|[ElementHandle]|[Object]|[Array]<[string]>|[Array]<[ElementHandle]>|[Array]<[Object]>> Options to select. If the `<select>` has the `multiple` attribute, all matching options are selected, otherwise only the first option matching one of the passed options is selected. String values are equivalent to `{value:'string'}`. Option is considered matching if all specified properties match.
   - `value` <[string]> Matches by `option.value`.
@@ -3488,7 +3488,7 @@ This methods attaches Playwright to an existing browser instance.
 #### browserType.devices
 - returns: <[Object]>
 
-Returns a list of devices to be used with [`browser.newContext(options)`](#browsernewcontextoptions) and [`browser.newPage(options)`](#browsernewpageoptions). Actual list of devices can be found in [src/deviceDescriptors.ts](https://github.com/Microsoft/playwright/blob/master/src/deviceDescriptors.ts).
+Returns a list of devices to be used with [`browser.newContext([options])`](#browsernewcontextoptions) and [`browser.newPage([options])`](#browsernewpageoptions). Actual list of devices can be found in [src/deviceDescriptors.ts](https://github.com/Microsoft/playwright/blob/master/src/deviceDescriptors.ts).
 
 ```js
 const { webkit } = require('playwright');
@@ -3640,7 +3640,7 @@ await browser.stopTracing();
 
 <!-- GEN:toc -->
 - [chromiumBrowser.createBrowserSession()](#chromiumbrowsercreatebrowsersession)
-- [chromiumBrowser.startTracing(page, [options])](#chromiumbrowserstarttracingpage-options)
+- [chromiumBrowser.startTracing([page, options])](#chromiumbrowserstarttracingpage-options)
 - [chromiumBrowser.stopTracing()](#chromiumbrowserstoptracing)
 <!-- GEN:stop -->
 <!-- GEN:toc-extends-Browser -->
@@ -3648,7 +3648,7 @@ await browser.stopTracing();
 - [browser.close()](#browserclose)
 - [browser.contexts()](#browsercontexts)
 - [browser.isConnected()](#browserisconnected)
-- [browser.newContext(options)](#browsernewcontextoptions)
+- [browser.newContext([options])](#browsernewcontextoptions)
 - [browser.newPage([options])](#browsernewpageoptions)
 <!-- GEN:stop -->
 
@@ -3656,7 +3656,7 @@ await browser.stopTracing();
 - returns: <[Promise]<[ChromiumSession]>> Promise that resolves to the newly created browser
 session.
 
-#### chromiumBrowser.startTracing(page, [options])
+#### chromiumBrowser.startTracing([page, options])
 - `page` <[Page]> Optional, if specified, tracing includes screenshots of the given page.
 - `options` <[Object]>
   - `path` <[string]> A path to write the trace file to.
@@ -3839,7 +3839,7 @@ Firefox browser instance does not expose Firefox-specific features.
 - [browser.close()](#browserclose)
 - [browser.contexts()](#browsercontexts)
 - [browser.isConnected()](#browserisconnected)
-- [browser.newContext(options)](#browsernewcontextoptions)
+- [browser.newContext([options])](#browsernewcontextoptions)
 - [browser.newPage([options])](#browsernewpageoptions)
 <!-- GEN:stop -->
 
@@ -3854,7 +3854,7 @@ WebKit browser instance does not expose WebKit-specific features.
 - [browser.close()](#browserclose)
 - [browser.contexts()](#browsercontexts)
 - [browser.isConnected()](#browserisconnected)
-- [browser.newContext(options)](#browsernewcontextoptions)
+- [browser.newContext([options])](#browsernewcontextoptions)
 - [browser.newPage([options])](#browsernewpageoptions)
 <!-- GEN:stop -->
 
diff --git a/src/chromium/crBrowser.ts b/src/chromium/crBrowser.ts
index 8c627439ce378..f9d78346cb84e 100644
--- a/src/chromium/crBrowser.ts
+++ b/src/chromium/crBrowser.ts
@@ -150,7 +150,7 @@ export class CRBrowser extends platform.EventEmitter implements Browser {
     return await this._connection.createBrowserSession();
   }
 
-  async startTracing(page: Page | undefined, options: { path?: string; screenshots?: boolean; categories?: string[]; } = {}) {
+  async startTracing(page?: Page, options: { path?: string; screenshots?: boolean; categories?: string[]; } = {}) {
     assert(!this._tracingRecording, 'Cannot start recording trace while already recording trace.');
     this._tracingClient = page ? (page._delegate as CRPage)._client : this._client;
 
diff --git a/utils/doclint/check_public_api/JSBuilder.js b/utils/doclint/check_public_api/JSBuilder.js
index 6fc09746982e2..37d6db7bba325 100644
--- a/utils/doclint/check_public_api/JSBuilder.js
+++ b/utils/doclint/check_public_api/JSBuilder.js
@@ -40,6 +40,7 @@ function checkSources(sources, externalDependencies) {
     options: {
       allowJs: true,
       target: ts.ScriptTarget.ESNext,
+      strict: true
     },
     rootNames: sources.map(source => source.filePath())
   });
@@ -152,15 +153,39 @@ function checkSources(sources, externalDependencies) {
     return parents;
   }
 
-  function serializeSymbol(symbol, circular = []) {
+  /**
+   * @param {ts.Symbol} symbol
+   * @param {string[]=} circular
+   * @param {boolean=} parentRequired
+   */
+  function serializeSymbol(symbol, circular = [], parentRequired = true) {
     const type = checker.getTypeOfSymbolAtLocation(symbol, symbol.valueDeclaration);
     const name = symbol.getName();
     if (symbol.valueDeclaration && symbol.valueDeclaration.dotDotDotToken) {
       const innerType = serializeType(type.typeArguments ? type.typeArguments[0] : type, circular);
       innerType.name = '...' + innerType.name;
-      return Documentation.Member.createProperty('...' + name, innerType);
+      const required = false;
+      return Documentation.Member.createProperty('...' + name, innerType, undefined, required);
     }
-    return Documentation.Member.createProperty(name, serializeType(type, circular));
+
+    const required = parentRequired && !typeHasUndefined(type);
+    return Documentation.Member.createProperty(name, serializeType(type, circular), undefined, required);
+  }
+
+  /**
+   * @param {!ts.Type} type
+   */
+  function typeHasUndefined(type) {
+    if (!type.isUnion())
+      return type.flags & ts.TypeFlags.Undefined;
+    return type.types.some(typeHasUndefined);
+  }
+
+  /**
+   * @param {!ts.Type} type
+   */
+  function isNotNullish(type) {
+    return !((type.flags & ts.TypeFlags.Undefined) || (type.flags & ts.TypeFlags.Null));
   }
 
   /**
@@ -208,7 +233,9 @@ function checkSources(sources, externalDependencies) {
       return new Documentation.Type('Object', properties);
     }
     if (type.isUnion() && (typeName.includes('|') || type.types.every(type => type.isStringLiteral() || type.intrinsicName === 'number'))) {
-      const types = type.types.map(type => serializeType(type, circular));
+      const types = type.types
+        .filter(isNotNullish)
+        .map(type => serializeType(type, circular));
       const name = types.map(type => type.name).join('|');
       const properties = [].concat(...types.map(type => type.properties));
       return new Documentation.Type(name.replace(/false\|true/g, 'boolean'), properties);
@@ -253,7 +280,7 @@ function checkSources(sources, externalDependencies) {
         continue;
       }
       const memberType = checker.getTypeOfSymbolAtLocation(member, member.valueDeclaration);
-      const signature = memberType.getCallSignatures()[0];
+      const signature = signatureForType(memberType);
       if (signature)
         members.push(serializeSignature(name, signature));
       else
@@ -263,12 +290,28 @@ function checkSources(sources, externalDependencies) {
     return new Documentation.Class(className, members);
   }
 
+  /**
+   * @param {ts.Type} type
+   */
+  function signatureForType(type) {
+    const signatures = type.getCallSignatures();
+    if (signatures.length)
+      return signatures[0];
+    if (type.isUnion()) {
+      const innerTypes = type.types.filter(isNotNullish);
+      if (innerTypes.length === 1)
+        return signatureForType(innerTypes[0]);
+    }
+    return null;
+  }
+
   /**
    * @param {string} name
    * @param {!ts.Signature} signature
    */
   function serializeSignature(name, signature) {
-    const parameters = signature.parameters.map(s => serializeSymbol(s));
+    const minArgumentCount = signature.minArgumentCount || 0;
+    const parameters = signature.parameters.map((s, index) => serializeSymbol(s, [], index < minArgumentCount));
     const returnType = serializeType(signature.getReturnType());
     return Documentation.Member.createMethod(name, parameters, returnType.name !== 'void' ? returnType : null);
   }
diff --git a/utils/doclint/check_public_api/MDBuilder.js b/utils/doclint/check_public_api/MDBuilder.js
index 0a726d28d1211..96da960499525 100644
--- a/utils/doclint/check_public_api/MDBuilder.js
+++ b/utils/doclint/check_public_api/MDBuilder.js
@@ -154,7 +154,7 @@ class MDOutline {
             returnType = parseProperty(element);
           } else if (element.matches('li') && element.firstChild.matches && element.firstChild.matches('code')) {
             const property = parseProperty(element);
-            property.required = !optionalparams.has(property.name);
+            property.required = !optionalparams.has(property.name) && !property.name.startsWith('...');
             args.push(property);
           } else if (element.matches('li') && element.firstChild.nodeType === Element.TEXT_NODE && element.firstChild.textContent.toLowerCase().startsWith('return')) {
             returnType = parseProperty(element);
diff --git a/utils/doclint/check_public_api/index.js b/utils/doclint/check_public_api/index.js
index defbcadead4b2..c7923720bf8a8 100644
--- a/utils/doclint/check_public_api/index.js
+++ b/utils/doclint/check_public_api/index.js
@@ -143,6 +143,13 @@ function compareDocumentations(actual, expected) {
         for (const arg of argsDiff.extra)
           text.push(`- Non-existing argument found: ${arg}`);
         errors.push(text.join('\n'));
+      } else {
+        for (const name of actualMethod.args.keys()) {
+          const actual = actualMethod.args.get(name);
+          const expected = expectedMethod.args.get(name);
+          if (actual.required !== expected.required)
+            errors.push(`${className}.${methodName}(): ${name} should be ${expected.required ? 'required' : 'optional'}`);
+        }
       }
 
       for (const arg of argsDiff.equal)
diff --git a/utils/doclint/check_public_api/test/js-builder-common/api.ts b/utils/doclint/check_public_api/test/js-builder-common/api.ts
index 5251e4fe17c8b..366471820fcba 100644
--- a/utils/doclint/check_public_api/test/js-builder-common/api.ts
+++ b/utils/doclint/check_public_api/test/js-builder-common/api.ts
@@ -4,7 +4,7 @@ class A {
   constructor(delegate) {
   }
 
-  get getter() {
+  get getter() : any {
     return null;
   }