diff --git a/.appveyor.yml b/.appveyor.yml
index 0ae212addd2..f441ec2b8f6 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -25,7 +25,7 @@ test_script:
   - where chromedriver
   - set CHROMEDRIVER=C:\Tools\WebDriver\chromedriver.exe
   - cargo test -p js-sys --target wasm32-unknown-unknown
-  - cargo test -p web-sys --target wasm32-unknown-unknown
+  - cargo test --manifest-path crates/web-sys/Cargo.toml --target wasm32-unknown-unknown --all-features
   - cargo test -p webidl-tests --target wasm32-unknown-unknown
 
 branches:
diff --git a/.travis.yml b/.travis.yml
index 6d48ccc924d..944e8ebe851 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -97,8 +97,15 @@ matrix:
         - *INSTALL_CHROMEDRIVER
       script:
         - export RUST_LOG=wasm_bindgen_test_runner
-        - CHROMEDRIVER=`pwd`/chromedriver cargo test -p web-sys --target wasm32-unknown-unknown
-        - GECKODRIVER=`pwd`/geckodriver cargo test -p web-sys --target wasm32-unknown-unknown
+        # Test out builds with just a few features
+        - cargo build --manifest-path crates/web-sys/Cargo.toml --target wasm32-unknown-unknown
+        - cargo build --manifest-path crates/web-sys/Cargo.toml --target wasm32-unknown-unknown --features Node
+        - cargo build --manifest-path crates/web-sys/Cargo.toml --target wasm32-unknown-unknown --features Element
+        - cargo build --manifest-path crates/web-sys/Cargo.toml --target wasm32-unknown-unknown --features Window
+
+        # Now run all the tests with all the features
+        - CHROMEDRIVER=`pwd`/chromedriver cargo test --manifest-path crates/web-sys/Cargo.toml --target wasm32-unknown-unknown --all-features
+        - GECKODRIVER=`pwd`/geckodriver cargo test --manifest-path crates/web-sys/Cargo.toml --target wasm32-unknown-unknown --all-features
       addons:
         firefox: latest
         chrome: stable
@@ -176,7 +183,10 @@ matrix:
         - cargo install-update -a
       script:
         - (cd guide && mdbook build)
-        - cargo doc --no-deps -p wasm-bindgen -p web-sys -p js-sys -p wasm-bindgen-futures
+        - cargo doc --no-deps
+        - cargo doc --no-deps --manifest-path crates/js-sys/Cargo.toml
+        - cargo doc --no-deps --manifest-path crates/futures/Cargo.toml
+        - cargo doc --no-deps --manifest-path crates/web-sys/Cargo.toml --all-features
         - mv target/doc guide/book/api
       deploy:
         provider: pages
diff --git a/crates/backend/src/defined.rs b/crates/backend/src/defined.rs
index f697b502b8d..bf0e22afdbc 100644
--- a/crates/backend/src/defined.rs
+++ b/crates/backend/src/defined.rs
@@ -77,6 +77,15 @@ where
     }
 }
 
+impl<'a, T: ImportedTypes> ImportedTypes for &'a T {
+    fn imported_types<F>(&self, f: &mut F)
+    where
+        F: FnMut(&Ident, ImportedTypeKind),
+    {
+        (*self).imported_types(f)
+    }
+}
+
 impl ImportedTypes for ast::Program {
     fn imported_types<F>(&self, f: &mut F)
     where
diff --git a/crates/backend/src/error.rs b/crates/backend/src/error.rs
index b0c7776362a..aecce6f0664 100644
--- a/crates/backend/src/error.rs
+++ b/crates/backend/src/error.rs
@@ -15,9 +15,12 @@ macro_rules! bail_span {
     )
 }
 
+#[derive(Debug)]
 pub struct Diagnostic {
     inner: Repr,
 }
+
+#[derive(Debug)]
 enum Repr {
     Single {
         text: String,
diff --git a/crates/backend/src/util.rs b/crates/backend/src/util.rs
index f0bf53e71bc..fcfb9e9ce78 100644
--- a/crates/backend/src/util.rs
+++ b/crates/backend/src/util.rs
@@ -103,6 +103,7 @@ pub fn wrap_import_function(function: ast::ImportFunction) -> ast::Import {
 ///
 /// Hashes the public field here along with a few cargo-set env vars to
 /// distinguish between runs of the procedural macro.
+#[derive(Debug)]
 pub struct ShortHash<T>(pub T);
 
 impl<T: Hash> fmt::Display for ShortHash<T> {
diff --git a/crates/web-sys/Cargo.toml b/crates/web-sys/Cargo.toml
index 5a30a50a514..2ec704af81a 100644
--- a/crates/web-sys/Cargo.toml
+++ b/crates/web-sys/Cargo.toml
@@ -22,3 +22,1156 @@ js-sys = { path = '../js-sys', version = '0.2.4' }
 futures = "0.1"
 wasm-bindgen-test = { path = '../test', version = '0.2.19' }
 wasm-bindgen-futures = { path = '../futures', version = '0.2.19' }
+
+# This list is generated by passing `__WASM_BINDGEN_DUMP_FEATURES=foo` when
+# compiling this crate which dumps the total list of features to a file called
+# `foo`.
+#
+# Each one of these features activates the corresponding type, allowing bindings
+# to be generated for it. Note that we may eventually add "groupings" of
+# features to enable a convenient set of features all at once. For now, though,
+# the features must all be manually activated.
+[features]
+AbortController = []
+AbortSignal = []
+AddEventListenerOptions = []
+AesDerivedKeyParams = []
+AesKeyAlgorithm = []
+AesKeyGenParams = []
+Algorithm = []
+AlignSetting = []
+AnalyserNode = []
+AnalyserOptions = []
+Animation = []
+AnimationEffect = []
+AnimationEvent = []
+AnimationEventInit = []
+AnimationPlayState = []
+AnimationPlaybackEvent = []
+AnimationPlaybackEventInit = []
+AnimationPropertyValueDetails = []
+AnimationTimeline = []
+AssignedNodesOptions = []
+AttestationConveyancePreference = []
+Attr = []
+AttributeNameValue = []
+AudioBuffer = []
+AudioBufferOptions = []
+AudioBufferSourceNode = []
+AudioBufferSourceOptions = []
+AudioConfiguration = []
+AudioContext = []
+AudioContextOptions = []
+AudioContextState = []
+AudioDestinationNode = []
+AudioListener = []
+AudioNode = []
+AudioNodeOptions = []
+AudioParam = []
+AudioParamMap = []
+AudioProcessingEvent = []
+AudioScheduledSourceNode = []
+AudioStreamTrack = []
+AudioTrack = []
+AudioTrackList = []
+AudioWorklet = []
+AudioWorkletGlobalScope = []
+AudioWorkletNode = []
+AudioWorkletNodeOptions = []
+AudioWorkletProcessor = []
+AuthenticationExtensionsClientInputs = []
+AuthenticationExtensionsClientOutputs = []
+AuthenticatorAssertionResponse = []
+AuthenticatorAttachment = []
+AuthenticatorAttestationResponse = []
+AuthenticatorResponse = []
+AuthenticatorSelectionCriteria = []
+AuthenticatorTransport = []
+AutoKeyword = []
+AutocompleteInfo = []
+BarProp = []
+BaseAudioContext = []
+BaseComputedKeyframe = []
+BaseKeyframe = []
+BasePropertyIndexedKeyframe = []
+BasicCardRequest = []
+BasicCardResponse = []
+BasicCardType = []
+BatteryManager = []
+BeforeUnloadEvent = []
+BinaryType = []
+BiquadFilterNode = []
+BiquadFilterOptions = []
+BiquadFilterType = []
+Blob = []
+BlobEvent = []
+BlobEventInit = []
+BlobPropertyBag = []
+BlockParsingOptions = []
+BoxQuadOptions = []
+BroadcastChannel = []
+BrowserElementDownloadOptions = []
+BrowserElementExecuteScriptOptions = []
+BrowserFeedWriter = []
+BrowserFindCaseSensitivity = []
+BrowserFindDirection = []
+Cache = []
+CacheBatchOperation = []
+CacheQueryOptions = []
+CacheStorage = []
+CacheStorageNamespace = []
+CanvasCaptureMediaStream = []
+CanvasGradient = []
+CanvasPattern = []
+CanvasRenderingContext2d = []
+CanvasWindingRule = []
+CaretChangedReason = []
+CaretPosition = []
+CaretStateChangedEventInit = []
+CdataSection = []
+ChannelCountMode = []
+ChannelInterpretation = []
+ChannelMergerNode = []
+ChannelMergerOptions = []
+ChannelPixelLayout = []
+ChannelPixelLayoutDataType = []
+ChannelSplitterNode = []
+ChannelSplitterOptions = []
+CharacterData = []
+CheckerboardReason = []
+CheckerboardReport = []
+CheckerboardReportService = []
+ChromeFilePropertyBag = []
+ChromeWorker = []
+Client = []
+ClientQueryOptions = []
+ClientType = []
+Clients = []
+ClipboardEvent = []
+ClipboardEventInit = []
+CloseEvent = []
+CloseEventInit = []
+CollectedClientData = []
+Comment = []
+CompositeOperation = []
+CompositionEvent = []
+CompositionEventInit = []
+ComputedEffectTiming = []
+ConnStatusDict = []
+ConnectionType = []
+ConsoleCounter = []
+ConsoleCounterError = []
+ConsoleEvent = []
+ConsoleInstance = []
+ConsoleInstanceOptions = []
+ConsoleLevel = []
+ConsoleLogLevel = []
+ConsoleProfileEvent = []
+ConsoleStackEntry = []
+ConsoleTimerError = []
+ConsoleTimerLogOrEnd = []
+ConsoleTimerStart = []
+ConstantSourceNode = []
+ConstantSourceOptions = []
+ConstrainBooleanParameters = []
+ConstrainDomStringParameters = []
+ConstrainDoubleRange = []
+ConstrainLongRange = []
+ContextAttributes2d = []
+ConvertCoordinateOptions = []
+ConvolverNode = []
+ConvolverOptions = []
+Credential = []
+CredentialCreationOptions = []
+CredentialRequestOptions = []
+CredentialsContainer = []
+Crypto = []
+CryptoKey = []
+CryptoKeyPair = []
+Csp = []
+CspPolicies = []
+CspReport = []
+CspReportProperties = []
+CssAnimation = []
+CssBoxType = []
+CssConditionRule = []
+CssCounterStyleRule = []
+CssFontFaceRule = []
+CssFontFeatureValuesRule = []
+CssGroupingRule = []
+CssImportRule = []
+CssKeyframeRule = []
+CssKeyframesRule = []
+CssMediaRule = []
+CssMozDocumentRule = []
+CssNamespaceRule = []
+CssPageRule = []
+CssPseudoElement = []
+CssRule = []
+CssRuleList = []
+CssStyleDeclaration = []
+CssStyleRule = []
+CssStyleSheet = []
+CssStyleSheetParsingMode = []
+CssSupportsRule = []
+CssTransition = []
+CustomElementRegistry = []
+CustomEvent = []
+CustomEventInit = []
+DataTransfer = []
+DataTransferItem = []
+DataTransferItemList = []
+DateTimeValue = []
+DecoderDoctorNotification = []
+DecoderDoctorNotificationType = []
+DedicatedWorkerGlobalScope = []
+DelayNode = []
+DelayOptions = []
+DeviceAccelerationInit = []
+DeviceLightEvent = []
+DeviceLightEventInit = []
+DeviceMotionEvent = []
+DeviceMotionEventInit = []
+DeviceOrientationEvent = []
+DeviceOrientationEventInit = []
+DeviceProximityEvent = []
+DeviceProximityEventInit = []
+DeviceRotationRateInit = []
+DhKeyDeriveParams = []
+DirectionSetting = []
+Directory = []
+DisplayNameOptions = []
+DisplayNameResult = []
+DistanceModelType = []
+DnsCacheDict = []
+DnsCacheEntry = []
+DnsLookupDict = []
+Document = []
+DocumentFragment = []
+DocumentTimeline = []
+DocumentTimelineOptions = []
+DocumentType = []
+DomError = []
+DomException = []
+DomImplementation = []
+DomMatrix = []
+DomMatrixReadOnly = []
+DomParser = []
+DomPoint = []
+DomPointInit = []
+DomPointReadOnly = []
+DomQuad = []
+DomQuadInit = []
+DomQuadJson = []
+DomRect = []
+DomRectInit = []
+DomRectList = []
+DomRectReadOnly = []
+DomRequest = []
+DomRequestReadyState = []
+DomStringList = []
+DomStringMap = []
+DomTokenList = []
+DomWindowResizeEventDetail = []
+DragEvent = []
+DragEventInit = []
+DynamicsCompressorNode = []
+DynamicsCompressorOptions = []
+EcKeyAlgorithm = []
+EcKeyGenParams = []
+EcKeyImportParams = []
+EcdhKeyDeriveParams = []
+EffectTiming = []
+Element = []
+ElementCreationOptions = []
+ElementDefinitionOptions = []
+EndingTypes = []
+ErrorEvent = []
+ErrorEventInit = []
+Event = []
+EventInit = []
+EventListenerOptions = []
+EventModifierInit = []
+EventSource = []
+EventSourceInit = []
+EventTarget = []
+ExtendableEvent = []
+ExtendableEventInit = []
+ExtendableMessageEvent = []
+ExtendableMessageEventInit = []
+FakePluginMimeEntry = []
+FetchEvent = []
+FetchEventInit = []
+FetchObserver = []
+FetchReadableStreamReadDataArray = []
+FetchReadableStreamReadDataDone = []
+FetchState = []
+File = []
+FileList = []
+FilePropertyBag = []
+FileReader = []
+FileReaderSync = []
+FileSystem = []
+FileSystemDirectoryEntry = []
+FileSystemDirectoryReader = []
+FileSystemEntry = []
+FileSystemFileEntry = []
+FileSystemFlags = []
+FillMode = []
+FlashClassification = []
+FlexLineGrowthState = []
+FocusEvent = []
+FocusEventInit = []
+FontFace = []
+FontFaceDescriptors = []
+FontFaceLoadStatus = []
+FontFaceSet = []
+FontFaceSetIteratorResult = []
+FontFaceSetLoadEvent = []
+FontFaceSetLoadEventInit = []
+FontFaceSetLoadStatus = []
+FormData = []
+FrameType = []
+FuzzingFunctions = []
+GainNode = []
+GainOptions = []
+Gamepad = []
+GamepadAxisMoveEvent = []
+GamepadAxisMoveEventInit = []
+GamepadButton = []
+GamepadButtonEvent = []
+GamepadButtonEventInit = []
+GamepadEvent = []
+GamepadEventInit = []
+GamepadHand = []
+GamepadHapticActuator = []
+GamepadHapticActuatorType = []
+GamepadMappingType = []
+GamepadPose = []
+GamepadServiceTest = []
+GetNotificationOptions = []
+GridDeclaration = []
+GridTrackState = []
+GroupedHistoryEventInit = []
+HalfOpenInfoDict = []
+HashChangeEvent = []
+HashChangeEventInit = []
+Headers = []
+HeadersGuardEnum = []
+HiddenPluginEventInit = []
+History = []
+HitRegionOptions = []
+HmacKeyAlgorithm = []
+HtmlAllCollection = []
+HtmlAnchorElement = []
+HtmlAreaElement = []
+HtmlAudioElement = []
+HtmlBaseElement = []
+HtmlBodyElement = []
+HtmlBrElement = []
+HtmlButtonElement = []
+HtmlCanvasElement = []
+HtmlCollection = []
+HtmlDListElement = []
+HtmlDataElement = []
+HtmlDataListElement = []
+HtmlDetailsElement = []
+HtmlDialogElement = []
+HtmlDirectoryElement = []
+HtmlDivElement = []
+HtmlDocument = []
+HtmlElement = []
+HtmlEmbedElement = []
+HtmlFieldSetElement = []
+HtmlFontElement = []
+HtmlFormControlsCollection = []
+HtmlFormElement = []
+HtmlFrameElement = []
+HtmlFrameSetElement = []
+HtmlHeadElement = []
+HtmlHeadingElement = []
+HtmlHrElement = []
+HtmlHtmlElement = []
+HtmlIFrameElement = []
+HtmlImageElement = []
+HtmlInputElement = []
+HtmlLabelElement = []
+HtmlLegendElement = []
+HtmlLiElement = []
+HtmlLinkElement = []
+HtmlMapElement = []
+HtmlMediaElement = []
+HtmlMenuElement = []
+HtmlMenuItemElement = []
+HtmlMetaElement = []
+HtmlMeterElement = []
+HtmlModElement = []
+HtmlOListElement = []
+HtmlObjectElement = []
+HtmlOptGroupElement = []
+HtmlOptionElement = []
+HtmlOptionsCollection = []
+HtmlOutputElement = []
+HtmlParagraphElement = []
+HtmlParamElement = []
+HtmlPictureElement = []
+HtmlPreElement = []
+HtmlProgressElement = []
+HtmlQuoteElement = []
+HtmlScriptElement = []
+HtmlSelectElement = []
+HtmlSlotElement = []
+HtmlSourceElement = []
+HtmlSpanElement = []
+HtmlStyleElement = []
+HtmlTableCaptionElement = []
+HtmlTableCellElement = []
+HtmlTableColElement = []
+HtmlTableElement = []
+HtmlTableRowElement = []
+HtmlTableSectionElement = []
+HtmlTemplateElement = []
+HtmlTextAreaElement = []
+HtmlTimeElement = []
+HtmlTitleElement = []
+HtmlTrackElement = []
+HtmlUListElement = []
+HtmlUnknownElement = []
+HtmlVideoElement = []
+HttpConnDict = []
+HttpConnInfo = []
+HttpConnectionElement = []
+IdbCursor = []
+IdbCursorDirection = []
+IdbCursorWithValue = []
+IdbDatabase = []
+IdbFactory = []
+IdbFileHandle = []
+IdbFileMetadataParameters = []
+IdbFileRequest = []
+IdbIndex = []
+IdbIndexParameters = []
+IdbKeyRange = []
+IdbLocaleAwareKeyRange = []
+IdbMutableFile = []
+IdbObjectStore = []
+IdbObjectStoreParameters = []
+IdbOpenDbOptions = []
+IdbOpenDbRequest = []
+IdbRequest = []
+IdbRequestReadyState = []
+IdbTransaction = []
+IdbTransactionMode = []
+IdbVersionChangeEvent = []
+IdbVersionChangeEventInit = []
+IdleDeadline = []
+IdleRequestOptions = []
+IirFilterNode = []
+ImageBitmap = []
+ImageBitmapFormat = []
+ImageBitmapRenderingContext = []
+ImageCapture = []
+ImageCaptureErrorEvent = []
+ImageCaptureErrorEventInit = []
+ImageData = []
+InputEvent = []
+InputEventInit = []
+InstallTriggerData = []
+IntersectionObserver = []
+IntersectionObserverEntry = []
+IntersectionObserverEntryInit = []
+IntersectionObserverInit = []
+IterableKeyAndValueResult = []
+IterableKeyOrValueResult = []
+IterationCompositeOperation = []
+JsonWebKey = []
+KeyAlgorithm = []
+KeyEvent = []
+KeyboardEvent = []
+KeyboardEventInit = []
+KeyframeEffect = []
+KeyframeEffectOptions = []
+L10nElement = []
+L10nValue = []
+LifecycleCallbacks = []
+LineAlignSetting = []
+LocalMediaStream = []
+LocaleInfo = []
+Location = []
+MediaCapabilities = []
+MediaCapabilitiesInfo = []
+MediaConfiguration = []
+MediaDecodingConfiguration = []
+MediaDecodingType = []
+MediaDeviceInfo = []
+MediaDeviceKind = []
+MediaDevices = []
+MediaElementAudioSourceNode = []
+MediaElementAudioSourceOptions = []
+MediaEncodingConfiguration = []
+MediaEncodingType = []
+MediaEncryptedEvent = []
+MediaError = []
+MediaKeyError = []
+MediaKeyMessageEvent = []
+MediaKeyMessageEventInit = []
+MediaKeyMessageType = []
+MediaKeyNeededEventInit = []
+MediaKeySession = []
+MediaKeySessionType = []
+MediaKeyStatus = []
+MediaKeyStatusMap = []
+MediaKeySystemAccess = []
+MediaKeySystemConfiguration = []
+MediaKeySystemMediaCapability = []
+MediaKeySystemStatus = []
+MediaKeys = []
+MediaKeysPolicy = []
+MediaKeysRequirement = []
+MediaList = []
+MediaQueryList = []
+MediaQueryListEvent = []
+MediaQueryListEventInit = []
+MediaRecorder = []
+MediaRecorderErrorEvent = []
+MediaRecorderErrorEventInit = []
+MediaRecorderOptions = []
+MediaSource = []
+MediaSourceEndOfStreamError = []
+MediaSourceEnum = []
+MediaSourceReadyState = []
+MediaStream = []
+MediaStreamAudioDestinationNode = []
+MediaStreamAudioSourceNode = []
+MediaStreamAudioSourceOptions = []
+MediaStreamConstraints = []
+MediaStreamEvent = []
+MediaStreamEventInit = []
+MediaStreamTrack = []
+MediaStreamTrackEvent = []
+MediaStreamTrackEventInit = []
+MediaStreamTrackState = []
+MediaTrackConstraintSet = []
+MediaTrackConstraints = []
+MediaTrackSettings = []
+MediaTrackSupportedConstraints = []
+MessageChannel = []
+MessageEvent = []
+MessageEventInit = []
+MessagePort = []
+MidiAccess = []
+MidiConnectionEvent = []
+MidiConnectionEventInit = []
+MidiInput = []
+MidiInputMap = []
+MidiMessageEvent = []
+MidiMessageEventInit = []
+MidiOptions = []
+MidiOutput = []
+MidiOutputMap = []
+MidiPort = []
+MidiPortConnectionState = []
+MidiPortDeviceState = []
+MidiPortType = []
+MimeType = []
+MimeTypeArray = []
+MouseEvent = []
+MouseEventInit = []
+MouseScrollEvent = []
+MozApplicationEventInit = []
+MozPacketDumpType = []
+MozPluginParameter = []
+MozRtcIceCandidate = []
+MozRtcPeerConnection = []
+MozRtcSessionDescription = []
+MozXmlHttpRequestParameters = []
+MutationEvent = []
+MutationObserver = []
+MutationObserverInit = []
+MutationObservingInfo = []
+MutationRecord = []
+NamedNodeMap = []
+NativeOsFileReadOptions = []
+NativeOsFileWriteAtomicOptions = []
+NavigationType = []
+Navigator = []
+NetworkCommandOptions = []
+NetworkInformation = []
+NetworkResultOptions = []
+Node = []
+NodeIterator = []
+NodeList = []
+Notification = []
+NotificationBehavior = []
+NotificationDirection = []
+NotificationEvent = []
+NotificationEventInit = []
+NotificationOptions = []
+NotificationPermission = []
+OfflineAudioCompletionEvent = []
+OfflineAudioCompletionEventInit = []
+OfflineAudioContext = []
+OfflineAudioContextOptions = []
+OfflineResourceList = []
+OffscreenCanvas = []
+OpenWindowEventDetail = []
+OptionalEffectTiming = []
+OrientationLockType = []
+OrientationType = []
+OscillatorNode = []
+OscillatorOptions = []
+OscillatorType = []
+OverSampleType = []
+PageTransitionEvent = []
+PageTransitionEventInit = []
+PaintRequest = []
+PaintRequestList = []
+PaintWorkletGlobalScope = []
+PannerNode = []
+PannerOptions = []
+PanningModelType = []
+Path2d = []
+PaymentAddress = []
+PaymentComplete = []
+PaymentMethodChangeEvent = []
+PaymentMethodChangeEventInit = []
+PaymentRequestUpdateEvent = []
+PaymentRequestUpdateEventInit = []
+PaymentResponse = []
+PcImplIceConnectionState = []
+PcImplIceGatheringState = []
+PcImplSignalingState = []
+PcObserverStateType = []
+Performance = []
+PerformanceEntry = []
+PerformanceEntryEventInit = []
+PerformanceEntryFilterOptions = []
+PerformanceMark = []
+PerformanceMeasure = []
+PerformanceNavigation = []
+PerformanceNavigationTiming = []
+PerformanceObserver = []
+PerformanceObserverEntryList = []
+PerformanceResourceTiming = []
+PerformanceServerTiming = []
+PerformanceTiming = []
+PeriodicWave = []
+PeriodicWaveConstraints = []
+PeriodicWaveOptions = []
+PermissionDescriptor = []
+PermissionName = []
+PermissionState = []
+PermissionStatus = []
+Permissions = []
+PlaybackDirection = []
+Plugin = []
+PluginArray = []
+PluginCrashedEventInit = []
+PointerEvent = []
+PointerEventInit = []
+PopStateEvent = []
+PopStateEventInit = []
+PopupBlockedEvent = []
+PopupBlockedEventInit = []
+PositionAlignSetting = []
+PositionOptions = []
+Presentation = []
+PresentationAvailability = []
+PresentationConnection = []
+PresentationConnectionAvailableEvent = []
+PresentationConnectionAvailableEventInit = []
+PresentationConnectionBinaryType = []
+PresentationConnectionCloseEvent = []
+PresentationConnectionCloseEventInit = []
+PresentationConnectionClosedReason = []
+PresentationConnectionList = []
+PresentationConnectionState = []
+PresentationReceiver = []
+PresentationRequest = []
+ProcessingInstruction = []
+ProfileTimelineLayerRect = []
+ProfileTimelineMarker = []
+ProfileTimelineMessagePortOperationType = []
+ProfileTimelineStackFrame = []
+ProfileTimelineWorkerOperationType = []
+ProgressEvent = []
+ProgressEventInit = []
+PromiseRejectionEvent = []
+PromiseRejectionEventInit = []
+PublicKeyCredential = []
+PublicKeyCredentialEntity = []
+PublicKeyCredentialParameters = []
+PublicKeyCredentialRpEntity = []
+PublicKeyCredentialType = []
+PushEncryptionKeyName = []
+PushEvent = []
+PushEventInit = []
+PushManager = []
+PushMessageData = []
+PushPermissionState = []
+PushSubscription = []
+PushSubscriptionInit = []
+PushSubscriptionJson = []
+PushSubscriptionKeys = []
+PushSubscriptionOptions = []
+PushSubscriptionOptionsInit = []
+RadioNodeList = []
+Range = []
+RcwnPerfStats = []
+RcwnStatus = []
+RecordingState = []
+ReferrerPolicy = []
+RegisterRequest = []
+RegisterResponse = []
+RegisteredKey = []
+RegistrationOptions = []
+Request = []
+RequestCache = []
+RequestCredentials = []
+RequestDestination = []
+RequestInit = []
+RequestMediaKeySystemAccessNotification = []
+RequestMode = []
+RequestRedirect = []
+Response = []
+ResponseInit = []
+ResponseType = []
+RsaOaepParams = []
+RsaOtherPrimesInfo = []
+RsaPssParams = []
+RtcAnswerOptions = []
+RtcBundlePolicy = []
+RtcCertificate = []
+RtcCertificateExpiration = []
+RtcCodecStats = []
+RtcConfiguration = []
+RtcDataChannel = []
+RtcDataChannelEvent = []
+RtcDataChannelEventInit = []
+RtcDataChannelInit = []
+RtcDataChannelState = []
+RtcDataChannelType = []
+RtcDegradationPreference = []
+RtcFecParameters = []
+RtcIceCandidate = []
+RtcIceCandidateInit = []
+RtcIceCandidatePairStats = []
+RtcIceCandidateStats = []
+RtcIceComponentStats = []
+RtcIceConnectionState = []
+RtcIceCredentialType = []
+RtcIceGatheringState = []
+RtcIceServer = []
+RtcIceTransportPolicy = []
+RtcIdentityAssertion = []
+RtcIdentityAssertionResult = []
+RtcIdentityProviderDetails = []
+RtcIdentityProviderOptions = []
+RtcIdentityValidationResult = []
+RtcInboundRtpStreamStats = []
+RtcLifecycleEvent = []
+RtcMediaStreamStats = []
+RtcMediaStreamTrackStats = []
+RtcOfferAnswerOptions = []
+RtcOfferOptions = []
+RtcOutboundRtpStreamStats = []
+RtcPeerConnection = []
+RtcPeerConnectionIceEvent = []
+RtcPeerConnectionIceEventInit = []
+RtcPriorityType = []
+RtcRtcpParameters = []
+RtcRtpCodecParameters = []
+RtcRtpContributingSource = []
+RtcRtpEncodingParameters = []
+RtcRtpHeaderExtensionParameters = []
+RtcRtpParameters = []
+RtcRtpReceiver = []
+RtcRtpSender = []
+RtcRtpSourceEntry = []
+RtcRtpSourceEntryType = []
+RtcRtpSynchronizationSource = []
+RtcRtxParameters = []
+RtcSdpType = []
+RtcSessionDescription = []
+RtcSessionDescriptionInit = []
+RtcSignalingState = []
+RtcStats = []
+RtcStatsIceCandidatePairState = []
+RtcStatsIceCandidateType = []
+RtcStatsReport = []
+RtcStatsReportInternal = []
+RtcStatsType = []
+RtcTrackEvent = []
+RtcTransportStats = []
+RtcdtmfSender = []
+RtcdtmfToneChangeEvent = []
+RtcdtmfToneChangeEventInit = []
+RtcrtpContributingSourceStats = []
+RtcrtpStreamStats = []
+Screen = []
+ScreenColorGamut = []
+ScreenLuminance = []
+ScreenOrientation = []
+ScriptProcessorNode = []
+ScrollAreaEvent = []
+ScrollBehavior = []
+ScrollIntoViewOptions = []
+ScrollLogicalPosition = []
+ScrollOptions = []
+ScrollRestoration = []
+ScrollSetting = []
+ScrollState = []
+ScrollToOptions = []
+ScrollViewChangeEventInit = []
+SecurityPolicyViolationEvent = []
+SecurityPolicyViolationEventDisposition = []
+SecurityPolicyViolationEventInit = []
+Selection = []
+ServerSocketOptions = []
+ServiceWorker = []
+ServiceWorkerContainer = []
+ServiceWorkerGlobalScope = []
+ServiceWorkerRegistration = []
+ServiceWorkerState = []
+ServiceWorkerUpdateViaCache = []
+ShadowRoot = []
+ShadowRootInit = []
+ShadowRootMode = []
+SharedWorker = []
+SharedWorkerGlobalScope = []
+SignResponse = []
+SocketElement = []
+SocketOptions = []
+SocketReadyState = []
+SocketsDict = []
+SourceBuffer = []
+SourceBufferAppendMode = []
+SourceBufferList = []
+SpeechGrammar = []
+SpeechGrammarList = []
+SpeechRecognition = []
+SpeechRecognitionAlternative = []
+SpeechRecognitionError = []
+SpeechRecognitionErrorCode = []
+SpeechRecognitionErrorInit = []
+SpeechRecognitionEvent = []
+SpeechRecognitionEventInit = []
+SpeechRecognitionResult = []
+SpeechRecognitionResultList = []
+SpeechSynthesis = []
+SpeechSynthesisErrorCode = []
+SpeechSynthesisErrorEvent = []
+SpeechSynthesisErrorEventInit = []
+SpeechSynthesisEvent = []
+SpeechSynthesisEventInit = []
+SpeechSynthesisUtterance = []
+SpeechSynthesisVoice = []
+StereoPannerNode = []
+StereoPannerOptions = []
+Storage = []
+StorageEstimate = []
+StorageEvent = []
+StorageEventInit = []
+StorageManager = []
+StorageType = []
+StyleRuleChangeEventInit = []
+StyleSheet = []
+StyleSheetApplicableStateChangeEventInit = []
+StyleSheetChangeEventInit = []
+StyleSheetList = []
+SubtleCrypto = []
+SupportedType = []
+SvgAngle = []
+SvgAnimateElement = []
+SvgAnimateMotionElement = []
+SvgAnimateTransformElement = []
+SvgAnimatedAngle = []
+SvgAnimatedBoolean = []
+SvgAnimatedEnumeration = []
+SvgAnimatedInteger = []
+SvgAnimatedLength = []
+SvgAnimatedLengthList = []
+SvgAnimatedNumber = []
+SvgAnimatedNumberList = []
+SvgAnimatedPreserveAspectRatio = []
+SvgAnimatedRect = []
+SvgAnimatedString = []
+SvgAnimatedTransformList = []
+SvgAnimationElement = []
+SvgBoundingBoxOptions = []
+SvgCircleElement = []
+SvgClipPathElement = []
+SvgComponentTransferFunctionElement = []
+SvgDefsElement = []
+SvgDescElement = []
+SvgElement = []
+SvgEllipseElement = []
+SvgFilterElement = []
+SvgForeignObjectElement = []
+SvgGeometryElement = []
+SvgGradientElement = []
+SvgGraphicsElement = []
+SvgImageElement = []
+SvgLength = []
+SvgLengthList = []
+SvgLineElement = []
+SvgLinearGradientElement = []
+SvgMarkerElement = []
+SvgMaskElement = []
+SvgMatrix = []
+SvgMetadataElement = []
+SvgNumber = []
+SvgNumberList = []
+SvgPathElement = []
+SvgPathSegList = []
+SvgPatternElement = []
+SvgPoint = []
+SvgPointList = []
+SvgPolygonElement = []
+SvgPolylineElement = []
+SvgPreserveAspectRatio = []
+SvgRadialGradientElement = []
+SvgRect = []
+SvgRectElement = []
+SvgScriptElement = []
+SvgSetElement = []
+SvgStopElement = []
+SvgStringList = []
+SvgStyleElement = []
+SvgSwitchElement = []
+SvgSymbolElement = []
+SvgTextContentElement = []
+SvgTextElement = []
+SvgTextPathElement = []
+SvgTextPositioningElement = []
+SvgTitleElement = []
+SvgTransform = []
+SvgTransformList = []
+SvgUnitTypes = []
+SvgUseElement = []
+SvgViewElement = []
+SvgZoomAndPan = []
+SvgaElement = []
+SvgfeBlendElement = []
+SvgfeColorMatrixElement = []
+SvgfeComponentTransferElement = []
+SvgfeCompositeElement = []
+SvgfeConvolveMatrixElement = []
+SvgfeDiffuseLightingElement = []
+SvgfeDisplacementMapElement = []
+SvgfeDistantLightElement = []
+SvgfeDropShadowElement = []
+SvgfeFloodElement = []
+SvgfeFuncAElement = []
+SvgfeFuncBElement = []
+SvgfeFuncGElement = []
+SvgfeFuncRElement = []
+SvgfeGaussianBlurElement = []
+SvgfeImageElement = []
+SvgfeMergeElement = []
+SvgfeMergeNodeElement = []
+SvgfeMorphologyElement = []
+SvgfeOffsetElement = []
+SvgfePointLightElement = []
+SvgfeSpecularLightingElement = []
+SvgfeSpotLightElement = []
+SvgfeTileElement = []
+SvgfeTurbulenceElement = []
+SvggElement = []
+SvgmPathElement = []
+SvgsvgElement = []
+SvgtSpanElement = []
+TcpReadyState = []
+TcpServerSocket = []
+TcpServerSocketEvent = []
+TcpServerSocketEventInit = []
+TcpSocket = []
+TcpSocketBinaryType = []
+TcpSocketErrorEvent = []
+TcpSocketErrorEventInit = []
+TcpSocketEvent = []
+TcpSocketEventInit = []
+Text = []
+TextDecodeOptions = []
+TextDecoder = []
+TextDecoderOptions = []
+TextEncoder = []
+TextMetrics = []
+TextTrack = []
+TextTrackCue = []
+TextTrackCueList = []
+TextTrackKind = []
+TextTrackList = []
+TextTrackMode = []
+TimeEvent = []
+TimeRanges = []
+Touch = []
+TouchEvent = []
+TouchEventInit = []
+TouchInit = []
+TouchList = []
+TrackEvent = []
+TrackEventInit = []
+TransitionEvent = []
+TransitionEventInit = []
+Transport = []
+TreeCellInfo = []
+TreeWalker = []
+U2f = []
+U2fClientData = []
+UdpMessageEventInit = []
+UdpOptions = []
+UiEvent = []
+UiEventInit = []
+Url = []
+UrlSearchParams = []
+UserProximityEvent = []
+UserProximityEventInit = []
+UserVerificationRequirement = []
+ValidityState = []
+VideoConfiguration = []
+VideoFacingModeEnum = []
+VideoPlaybackQuality = []
+VideoStreamTrack = []
+VideoTrack = []
+VideoTrackList = []
+VrDisplay = []
+VrDisplayCapabilities = []
+VrEye = []
+VrEyeParameters = []
+VrFieldOfView = []
+VrFrameData = []
+VrLayer = []
+VrMockController = []
+VrMockDisplay = []
+VrPose = []
+VrServiceTest = []
+VrStageParameters = []
+VrSubmitFrameResult = []
+VttCue = []
+VttRegion = []
+WaveShaperNode = []
+WaveShaperOptions = []
+WebGl2RenderingContext = []
+WebGlActiveInfo = []
+WebGlBuffer = []
+WebGlContextAttributes = []
+WebGlContextEvent = []
+WebGlContextEventInit = []
+WebGlFramebuffer = []
+WebGlPowerPreference = []
+WebGlProgram = []
+WebGlQuery = []
+WebGlRenderbuffer = []
+WebGlRenderingContext = []
+WebGlSampler = []
+WebGlShader = []
+WebGlShaderPrecisionFormat = []
+WebGlSync = []
+WebGlTexture = []
+WebGlTransformFeedback = []
+WebGlUniformLocation = []
+WebGlVertexArrayObject = []
+WebGpu = []
+WebGpuAdapter = []
+WebGpuAdapterDescriptor = []
+WebGpuAttachmentState = []
+WebGpuAttachmentStateDescriptor = []
+WebGpuBindGroup = []
+WebGpuBindGroupBinding = []
+WebGpuBindGroupDescriptor = []
+WebGpuBindGroupLayout = []
+WebGpuBindGroupLayoutDescriptor = []
+WebGpuBinding = []
+WebGpuBindingType = []
+WebGpuBlendDescriptor = []
+WebGpuBlendFactor = []
+WebGpuBlendOperation = []
+WebGpuBlendState = []
+WebGpuBlendStateDescriptor = []
+WebGpuBuffer = []
+WebGpuBufferBinding = []
+WebGpuBufferDescriptor = []
+WebGpuBufferUsage = []
+WebGpuColorWriteBits = []
+WebGpuCommandBuffer = []
+WebGpuCommandEncoder = []
+WebGpuCommandEncoderDescriptor = []
+WebGpuCompareFunction = []
+WebGpuComputePipeline = []
+WebGpuComputePipelineDescriptor = []
+WebGpuDepthStencilState = []
+WebGpuDepthStencilStateDescriptor = []
+WebGpuDevice = []
+WebGpuDeviceDescriptor = []
+WebGpuExtensions = []
+WebGpuFence = []
+WebGpuFilterMode = []
+WebGpuIndexFormat = []
+WebGpuInputState = []
+WebGpuInputStateDescriptor = []
+WebGpuInputStepMode = []
+WebGpuLimits = []
+WebGpuLoadOp = []
+WebGpuLogEntry = []
+WebGpuLogEntryType = []
+WebGpuObjectStatus = []
+WebGpuPipelineDescriptorBase = []
+WebGpuPipelineLayout = []
+WebGpuPipelineLayoutDescriptor = []
+WebGpuPipelineStageDescriptor = []
+WebGpuPowerPreference = []
+WebGpuPrimitiveTopology = []
+WebGpuQueue = []
+WebGpuRenderPassAttachmentDescriptor = []
+WebGpuRenderPassDescriptor = []
+WebGpuRenderPipeline = []
+WebGpuRenderPipelineDescriptor = []
+WebGpuSampler = []
+WebGpuSamplerDescriptor = []
+WebGpuShaderModule = []
+WebGpuShaderModuleDescriptor = []
+WebGpuShaderStage = []
+WebGpuShaderStageBit = []
+WebGpuStencilOperation = []
+WebGpuStencilStateFaceDescriptor = []
+WebGpuStoreOp = []
+WebGpuSwapChain = []
+WebGpuSwapChainDescriptor = []
+WebGpuTexture = []
+WebGpuTextureDescriptor = []
+WebGpuTextureDimension = []
+WebGpuTextureFormat = []
+WebGpuTextureUsage = []
+WebGpuTextureView = []
+WebGpuTextureViewDescriptor = []
+WebGpuVertexAttributeDescriptor = []
+WebGpuVertexFormat = []
+WebGpuVertexInputDescriptor = []
+WebKitCssMatrix = []
+WebSocket = []
+WebSocketDict = []
+WebSocketElement = []
+WebrtcGlobalStatisticsReport = []
+WheelEvent = []
+WheelEventInit = []
+WidevineCdmManifest = []
+Window = []
+WindowClient = []
+Worker = []
+WorkerDebuggerGlobalScope = []
+WorkerGlobalScope = []
+WorkerLocation = []
+WorkerNavigator = []
+WorkerOptions = []
+Worklet = []
+WorkletGlobalScope = []
+XPathExpression = []
+XPathResult = []
+XmlDocument = []
+XmlHttpRequest = []
+XmlHttpRequestEventTarget = []
+XmlHttpRequestResponseType = []
+XmlHttpRequestUpload = []
+XmlSerializer = []
+XsltProcessor = []
diff --git a/crates/web-sys/README.md b/crates/web-sys/README.md
index d08fc0dab90..15b763dd344 100644
--- a/crates/web-sys/README.md
+++ b/crates/web-sys/README.md
@@ -1,9 +1,20 @@
 # `web-sys`
 
+[Documentation](https://rustwasm.github.io/wasm-bindgen/api/web_sys/)
+
 Raw bindings to Web APIs for projects using `wasm-bindgen`.
 
 The book: https://rustwasm.github.io/wasm-bindgen/web-sys.html
 
+## Crate features
+
+This crate by default contains very little when compiled as almost all of its
+exposed APIs are gated by Cargo features. The exhaustive list of features can be
+found in `crates/web-sys/Cargo.toml`, but the rule of thumb for `web-sys` is
+that each type has its own cargo feature (named after the type). Using an API
+requires enabling the features for all types used in the API, and APIs should
+mention in the documentation what features they require.
+
 ## Tested WebIDL bindings
 
 Below is a list of all the WebIDL files we want to generate bindings for, with a `x` where the
diff --git a/crates/web-sys/build.rs b/crates/web-sys/build.rs
index 5eef5158c1e..3eb3a10a151 100644
--- a/crates/web-sys/build.rs
+++ b/crates/web-sys/build.rs
@@ -6,10 +6,11 @@ extern crate sourcefile;
 
 use failure::{Fail, ResultExt};
 use sourcefile::SourceFile;
+use std::collections::HashSet;
 use std::env;
 use std::ffi::OsStr;
 use std::fs;
-use std::path;
+use std::path::{self, PathBuf};
 use std::process::{self, Command};
 
 fn main() {
@@ -41,7 +42,40 @@ fn try_main() -> Result<(), failure::Error> {
             .with_context(|_| format!("reading contents of file \"{}\"", path.display()))?;
     }
 
-    let bindings = match wasm_bindgen_webidl::compile(&source.contents) {
+    // Read our manifest, learn all `[feature]` directives with "toml parsing".
+    // Use all these names to match against environment variables set by Cargo
+    // to figure out which features are activated to we can pass that down to
+    // the webidl compiler.
+    let manifest_dir = PathBuf::from(env::var_os("CARGO_MANIFEST_DIR").unwrap());
+    let manifest = fs::read_to_string(manifest_dir.join("Cargo.toml"))?;
+    let features = manifest.lines().skip_while(|f| !f.starts_with("[features]"));
+
+    let enabled_features = env::vars()
+        .map(|p| p.0)
+        .filter(|p| p.starts_with("CARGO_FEATURE_"))
+        .map(|mut p| {
+            p.drain(0.."CARGO_FEATURE_".len());
+            p
+        })
+        .collect::<HashSet<_>>();
+
+    let mut allowed = Vec::new();
+    for feature in features.filter(|f| !f.starts_with("#") && !f.starts_with("[")) {
+        let mut parts = feature.split('=');
+        let name = parts.next().unwrap().trim();
+        if enabled_features.contains(&name.to_uppercase()) {
+            allowed.push(name);
+        }
+    }
+
+    // If we're printing all features don't filter anything
+    let allowed = if env::var("__WASM_BINDGEN_DUMP_FEATURES").is_ok() {
+        None
+    } else {
+        Some(&allowed[..])
+    };
+
+    let bindings = match wasm_bindgen_webidl::compile(&source.contents, allowed) {
         Ok(bindings) => bindings,
         Err(e) => match e.kind() {
             wasm_bindgen_webidl::ErrorKind::ParsingWebIDLSourcePos(pos) => {
diff --git a/crates/web-sys/src/lib.rs b/crates/web-sys/src/lib.rs
index 51ab34250e1..4c4f6dca9bb 100755
--- a/crates/web-sys/src/lib.rs
+++ b/crates/web-sys/src/lib.rs
@@ -1,3 +1,16 @@
+//! Raw API bindings for Web APIs
+//!
+//! This is a procedurally generated crate from browser WebIDL which provides a
+//! binding to all APIs that browser provide on the web.
+//!
+//! This crate by default contains very little when compiled as almost all of
+//! its exposed APIs are gated by Cargo features. The exhaustive list of
+//! features can be found in `crates/web-sys/Cargo.toml`, but the rule of thumb
+//! for `web-sys` is that each type has its own cargo feature (named after the
+//! type). Using an API requires enabling the features for all types used in the
+//! API, and APIs should mention in the documentation what features they
+//! require.
+
 #![doc(html_root_url = "https://docs.rs/web-sys/0.2")]
 
 extern crate wasm_bindgen;
diff --git a/crates/webidl-tests/build.rs b/crates/webidl-tests/build.rs
index 609efba1bbb..d9042613015 100644
--- a/crates/webidl-tests/build.rs
+++ b/crates/webidl-tests/build.rs
@@ -17,7 +17,7 @@ fn main() {
     let out_dir = PathBuf::from(env::var_os("OUT_DIR").unwrap());
     for (i, (idl, path)) in idls.enumerate() {
         println!("processing {:?}", path);
-        let mut generated_rust = wasm_bindgen_webidl::compile(&idl).unwrap();
+        let mut generated_rust = wasm_bindgen_webidl::compile(&idl, None).unwrap();
 
         let out_file = out_dir.join(path.file_name().unwrap())
             .with_extension("rs");
diff --git a/crates/webidl/src/first_pass.rs b/crates/webidl/src/first_pass.rs
index 39534791c4c..3762ad141cc 100644
--- a/crates/webidl/src/first_pass.rs
+++ b/crates/webidl/src/first_pass.rs
@@ -10,6 +10,7 @@
 use std::cmp::Ordering;
 use std::collections::{BTreeMap, BTreeSet};
 
+use proc_macro2::Ident;
 use weedle::{DictionaryDefinition, PartialDictionaryDefinition};
 use weedle::argument::Argument;
 use weedle::attribute::*;
@@ -24,6 +25,7 @@ use util;
 /// Collection of constructs that may use partial.
 #[derive(Default)]
 pub(crate) struct FirstPassRecord<'src> {
+    pub(crate) builtin_idents: BTreeSet<Ident>,
     pub(crate) interfaces: BTreeMap<&'src str, InterfaceData<'src>>,
     pub(crate) enums: BTreeMap<&'src str, &'src weedle::EnumDefinition<'src>>,
     /// The mixins, mapping their name to the webidl ast node for the mixin.
@@ -701,8 +703,10 @@ impl<'a> FirstPassRecord<'a> {
             Some(class) => class,
             None => return,
         };
-        if set.insert(camel_case_ident(superclass)) {
-            self.fill_superclasses(superclass, set);
+        if self.interfaces.contains_key(superclass) {
+            if set.insert(camel_case_ident(superclass)) {
+                self.fill_superclasses(superclass, set);
+            }
         }
     }
 
diff --git a/crates/webidl/src/lib.rs b/crates/webidl/src/lib.rs
index 5023763e9ff..b450acfbe78 100644
--- a/crates/webidl/src/lib.rs
+++ b/crates/webidl/src/lib.rs
@@ -29,18 +29,16 @@ mod idl_type;
 mod util;
 mod error;
 
-use std::collections::BTreeSet;
+use std::collections::{BTreeSet, HashSet, BTreeMap};
+use std::env;
 use std::fs;
-use std::io::{self, Read};
 use std::iter::FromIterator;
-use std::path::Path;
 
 use backend::ast;
 use backend::TryToTokens;
 use backend::defined::{ImportedTypeDefinitions, RemoveUndefinedImports};
 use backend::defined::ImportedTypeReferences;
 use backend::util::{ident_ty, rust_ident, raw_ident, wrap_import_function};
-use failure::ResultExt;
 use proc_macro2::{Ident, Span};
 use weedle::attribute::{ExtendedAttributeList};
 use weedle::dictionary::DictionaryMember;
@@ -52,17 +50,10 @@ use idl_type::ToIdlType;
 
 pub use error::{Error, ErrorKind, Result};
 
-/// Parse the WebIDL at the given path into a wasm-bindgen AST.
-fn parse_file(webidl_path: &Path) -> Result<backend::ast::Program> {
-    let file = fs::File::open(webidl_path).context(ErrorKind::OpeningWebIDLFile)?;
-    let mut file = io::BufReader::new(file);
-    let mut source = String::new();
-    file.read_to_string(&mut source).context(ErrorKind::ReadingWebIDLFile)?;
-    parse(&source)
-}
-
 /// Parse a string of WebIDL source text into a wasm-bindgen AST.
-fn parse(webidl_source: &str) -> Result<backend::ast::Program> {
+fn parse(webidl_source: &str, allowed_types: Option<&[&str]>)
+    -> Result<backend::ast::Program>
+{
     let definitions = match weedle::parse(webidl_source) {
         Ok(def) => def,
         Err(e) => {
@@ -84,10 +75,23 @@ fn parse(webidl_source: &str) -> Result<backend::ast::Program> {
         }
     };
 
-    let mut first_pass_record = Default::default();
+    let mut first_pass_record: FirstPassRecord = Default::default();
+    first_pass_record.builtin_idents = builtin_idents();
     definitions.first_pass(&mut first_pass_record, ())?;
     let mut program = Default::default();
 
+    // Prune out everything in the `first_pass_record` which isn't allowed, or
+    // is otherwise gated from not actually being generated.
+    if let Some(allowed_types) = allowed_types {
+        let allowed = allowed_types.iter().cloned().collect::<HashSet<_>>();
+        let filter = |name: &&str| {
+            allowed.contains(&camel_case_ident(name)[..])
+        };
+        retain(&mut first_pass_record.enums, &filter);
+        retain(&mut first_pass_record.dictionaries, &filter);
+        retain(&mut first_pass_record.interfaces, &filter);
+    }
+
     for e in first_pass_record.enums.values() {
         first_pass_record.append_enum(&mut program, e);
     }
@@ -104,43 +108,70 @@ fn parse(webidl_source: &str) -> Result<backend::ast::Program> {
     Ok(program)
 }
 
-/// Compile the given WebIDL file into Rust source text containing
-/// `wasm-bindgen` bindings to the things described in the WebIDL.
-pub fn compile_file(webidl_path: &Path) -> Result<String> {
-    let ast = parse_file(webidl_path)?;
-    Ok(compile_ast(ast))
+fn retain<K: Copy + Ord, V>(
+    map: &mut BTreeMap<K, V>,
+    mut filter: impl FnMut(&K) -> bool,
+) {
+    let mut to_remove = Vec::new();
+    for k in map.keys() {
+        if !filter(k) {
+            to_remove.push(*k);
+        }
+    }
+    for k in to_remove {
+        map.remove(&k);
+    }
 }
 
 /// Compile the given WebIDL source text into Rust source text containing
 /// `wasm-bindgen` bindings to the things described in the WebIDL.
-pub fn compile(webidl_source: &str) -> Result<String> {
-    let ast = parse(webidl_source)?;
+pub fn compile(
+    webidl_source: &str,
+    allowed_types: Option<&[&str]>,
+) -> Result<String> {
+    let ast = parse(webidl_source, allowed_types)?;
     Ok(compile_ast(ast))
 }
 
-/// Run codegen on the AST to generate rust code.
-fn compile_ast(mut ast: backend::ast::Program) -> String {
-    // Iteratively prune all entries from the AST which reference undefined
-    // fields. Each pass may remove definitions of types and so we need to
-    // reexecute this pass to see if we need to keep removing types until we
-    // reach a steady state.
-    let builtin = BTreeSet::from_iter(
+fn builtin_idents() -> BTreeSet<Ident> {
+    BTreeSet::from_iter(
         vec![
             "str", "char", "bool", "JsValue", "u8", "i8", "u16", "i16", "u32", "i32", "u64", "i64",
             "usize", "isize", "f32", "f64", "Result", "String", "Vec", "Option",
             "ArrayBuffer", "Object", "Promise",
         ].into_iter()
             .map(|id| proc_macro2::Ident::new(id, proc_macro2::Span::call_site())),
-    );
+    )
+}
+
+/// Run codegen on the AST to generate rust code.
+fn compile_ast(mut ast: backend::ast::Program) -> String {
+    // Iteratively prune all entries from the AST which reference undefined
+    // fields. Each pass may remove definitions of types and so we need to
+    // reexecute this pass to see if we need to keep removing types until we
+    // reach a steady state.
+    let builtin = builtin_idents();
+    let mut all_definitions = BTreeSet::new();
+    let track = env::var_os("__WASM_BINDGEN_DUMP_FEATURES");
     loop {
         let mut defined = builtin.clone();
         ast.imported_type_definitions(&mut |id| {
             defined.insert(id.clone());
+            if track.is_some() {
+                all_definitions.insert(id.clone());
+            }
         });
         if !ast.remove_undefined_imports(&|id| defined.contains(id)) {
             break
         }
     }
+    if let Some(path) = track {
+        let contents = all_definitions.into_iter()
+            .map(|s| format!("{} = []", s))
+            .collect::<Vec<_>>()
+            .join("\n");
+        fs::write(path, contents).unwrap();
+    }
 
     let mut tokens = proc_macro2::TokenStream::new();
     if let Err(e) = ast.try_to_tokens(&mut tokens) {
@@ -380,26 +411,29 @@ impl<'src> FirstPassRecord<'src> {
         name: &'src str,
         data: &InterfaceData<'src>,
     ) {
-        let doc_comment = Some(format!(
+        let mut doc_comment = Some(format!(
             "The `{}` object\n\n{}",
             name,
             mdn_doc(name, None),
         ));
+        let mut import_type = backend::ast::ImportType {
+            vis: public(),
+            rust_name: rust_ident(camel_case_ident(name).as_str()),
+            js_name: name.to_string(),
+            attrs: Vec::new(),
+            doc_comment: None,
+            instanceof_shim: format!("__widl_instanceof_{}", name),
+            extends: self.all_superclasses(name)
+                .map(|name| Ident::new(&name, Span::call_site()))
+                .collect(),
+        };
+        self.append_required_features_doc(&import_type, &mut doc_comment);
+        import_type.doc_comment = doc_comment;
 
         program.imports.push(backend::ast::Import {
             module: None,
             js_namespace: None,
-            kind: backend::ast::ImportKind::Type(backend::ast::ImportType {
-                vis: public(),
-                rust_name: rust_ident(camel_case_ident(name).as_str()),
-                js_name: name.to_string(),
-                attrs: Vec::new(),
-                doc_comment,
-                instanceof_shim: format!("__widl_instanceof_{}", name),
-                extends: self.all_superclasses(name)
-                    .map(|name| Ident::new(&name, Span::call_site()))
-                    .collect(),
-            }),
+            kind: backend::ast::ImportKind::Type(import_type),
         });
 
         for (id, op_data) in data.operations.iter() {
@@ -473,7 +507,7 @@ impl<'src> FirstPassRecord<'src> {
             .map(|interface_data| interface_data.global)
             .unwrap_or(false);
 
-        for import_function in self.create_getter(
+        for mut import_function in self.create_getter(
             identifier,
             &type_.type_,
             self_name,
@@ -482,11 +516,14 @@ impl<'src> FirstPassRecord<'src> {
             attrs,
             container_attrs,
         ) {
+            let mut doc = import_function.doc_comment.take();
+            self.append_required_features_doc(&import_function, &mut doc);
+            import_function.doc_comment = doc;
             program.imports.push(wrap_import_function(import_function));
         }
 
         if !readonly {
-            for import_function in self.create_setter(
+            for mut import_function in self.create_setter(
                 identifier,
                 &type_.type_,
                 self_name,
@@ -495,6 +532,9 @@ impl<'src> FirstPassRecord<'src> {
                 attrs,
                 container_attrs,
             ) {
+                let mut doc = import_function.doc_comment.take();
+                self.append_required_features_doc(&import_function, &mut doc);
+                import_function.doc_comment = doc;
                 program.imports.push(wrap_import_function(import_function));
             }
         }
@@ -535,7 +575,7 @@ impl<'src> FirstPassRecord<'src> {
         };
         let doc = match id {
             OperationId::Constructor(_) |
-            OperationId::Operation(None) => None,
+            OperationId::Operation(None) => Some(String::new()),
             OperationId::Operation(Some(name)) => {
                 Some(format!(
                     "The `{}()` method\n\n{}",
@@ -555,8 +595,39 @@ impl<'src> FirstPassRecord<'src> {
         };
         let attrs = data.definition_attributes;
         for mut method in self.create_imports(attrs, kind, id, op_data) {
-            method.doc_comment = doc.clone();
+            let mut doc = doc.clone();
+            self.append_required_features_doc(&method, &mut doc);
+            method.doc_comment = doc;
             program.imports.push(wrap_import_function(method));
         }
     }
+
+    fn append_required_features_doc(
+        &self,
+        item: impl ImportedTypeReferences,
+        doc: &mut Option<String>,
+    ) {
+        let doc = match doc {
+            Some(doc) => doc,
+            None => return,
+        };
+        let mut required = BTreeSet::new();
+        item.imported_type_references(&mut |f| {
+            if !self.builtin_idents.contains(f) {
+                required.insert(f.clone());
+            }
+        });
+        if required.len() == 0 {
+            return
+        }
+        let list = required.iter()
+            .map(|ident| format!("`{}`", ident))
+            .collect::<Vec<_>>()
+            .join(", ");
+        doc.push_str(&format!(
+            "\n\n*This function requires the following crate features \
+             to be activated: {}*",
+            list,
+        ));
+    }
 }
diff --git a/crates/webidl/src/util.rs b/crates/webidl/src/util.rs
index e583fcf3ba5..8c330b55066 100644
--- a/crates/webidl/src/util.rs
+++ b/crates/webidl/src/util.rs
@@ -53,7 +53,7 @@ pub fn mdn_doc(class: &str, method: Option<&str>) -> String {
     if let Some(method) = method {
         link.push_str(&format!("/{}", method));
     }
-    format!("[Documentation]({})", link).into()
+    format!("[MDN Documentation]({})", link).into()
 }
 
 // Array type is borrowed for arguments (`&[T]`) and owned for return value (`Vec<T>`).
@@ -401,13 +401,23 @@ impl<'src> FirstPassRecord<'src> {
     {
         // First up, prune all signatures that reference unsupported arguments.
         // We won't consider these until said arguments are implemented.
+        //
+        // Note that we handle optional arguments as well. Optional arguments
+        // should only appear at the end of argument lists and when we see one
+        // we can simply push our signature so far onto the list for the
+        // signature where that and all remaining optional arguments are
+        // undefined.
         let mut signatures = Vec::new();
         'outer:
         for signature in data.signatures.iter() {
             let mut idl_args = Vec::with_capacity(signature.args.len());
-            for arg in signature.args.iter() {
+            for (i, arg) in signature.args.iter().enumerate() {
+                if arg.optional {
+                    assert!(signature.args[i..].iter().all(|a| a.optional));
+                    signatures.push((signature, idl_args.clone()));
+                }
                 match arg.ty.to_idl_type(self) {
-                    Some(t) => idl_args.push((t, arg)),
+                    Some(t) => idl_args.push(t),
                     None => continue 'outer,
                 }
             }
@@ -434,23 +444,7 @@ impl<'src> FirstPassRecord<'src> {
                 args: Vec::with_capacity(signature.args.len()),
             });
 
-            for (i, (idl_type, arg)) in idl_args.iter().enumerate() {
-                // If this is an optional argument, then all remaining arguments
-                // should also be optional (if any). This means that all the
-                // signatures we've built up so far are valid signatures because
-                // we're just going to omit all the future arguments. As a
-                // result we duplicate all the previous signatures we've made in
-                // the list. The duplicates will be modified in-place below.
-                if arg.optional {
-                    assert!(signature.args[i..].iter().all(|a| a.optional));
-                    let end = actual_signatures.len();
-                    for j in start..end {
-                        let sig = actual_signatures[j].clone();
-                        actual_signatures.push(sig);
-                    }
-                    start = end;
-                }
-
+            for (i, idl_type) in idl_args.iter().enumerate() {
                 // small sanity check
                 assert!(start < actual_signatures.len());
                 for sig in actual_signatures[start..].iter() {
diff --git a/examples/canvas/Cargo.toml b/examples/canvas/Cargo.toml
index 9012930d90a..2f3420b02f4 100644
--- a/examples/canvas/Cargo.toml
+++ b/examples/canvas/Cargo.toml
@@ -9,4 +9,13 @@ crate-type = ["cdylib"]
 [dependencies]
 js-sys = { path = "../../crates/js-sys" }
 wasm-bindgen = { path = "../.." }
-web-sys = { path = "../../crates/web-sys" }
+
+[dependencies.web-sys]
+path = "../../crates/web-sys"
+features = [
+  'CanvasRenderingContext2d',
+  'Document',
+  'Element',
+  'HtmlCanvasElement',
+  'Window',
+]
diff --git a/examples/fetch/Cargo.toml b/examples/fetch/Cargo.toml
index ef6df418a5d..6203271070e 100644
--- a/examples/fetch/Cargo.toml
+++ b/examples/fetch/Cargo.toml
@@ -10,7 +10,17 @@ crate-type = ["cdylib"]
 futures = "0.1.20"
 wasm-bindgen = { path = "../..", features = ["serde-serialize"]  }
 js-sys = { path = "../../crates/js-sys" }
-web-sys = { path = "../../crates/web-sys" }
 wasm-bindgen-futures = { path = "../../crates/futures" }
 serde = "^1.0.59"
-serde_derive = "^1.0.59"
\ No newline at end of file
+serde_derive = "^1.0.59"
+
+[dependencies.web-sys]
+path = "../../crates/web-sys"
+features = [
+  'Headers',
+  'Request',
+  'RequestInit',
+  'RequestMode',
+  'Response',
+  'Window',
+]
diff --git a/examples/webaudio/Cargo.toml b/examples/webaudio/Cargo.toml
index 6d71cc84ac2..9f1f07f0c48 100644
--- a/examples/webaudio/Cargo.toml
+++ b/examples/webaudio/Cargo.toml
@@ -8,4 +8,17 @@ crate-type = ["cdylib"]
 
 [dependencies]
 wasm-bindgen = { path = "../.." }
-web-sys = { path = "../../crates/web-sys" }
\ No newline at end of file
+
+[dependencies.web-sys]
+path = "../../crates/web-sys"
+features = [
+  'AudioContext',
+  'AudioDestinationNode',
+  'AudioNode',
+  'AudioParam',
+  'AudioScheduledSourceNode',
+  'BaseAudioContext',
+  'GainNode',
+  'OscillatorNode',
+  'OscillatorType',
+]
diff --git a/guide/src/web-sys/overview.md b/guide/src/web-sys/overview.md
index 7b80faf1a76..96efa586ec0 100644
--- a/guide/src/web-sys/overview.md
+++ b/guide/src/web-sys/overview.md
@@ -10,17 +10,10 @@ The `web-sys` crate has this file and directory layout:
 ├── src
 │   └── lib.rs
 └── webidls
-    ├── available
-    │   └── ...
     └── enabled
         └── ...
 ```
 
-### `webidls/available/*.webidl`
-
-These are all the different WebIDL definitions we intend to support, but don't
-yet. At the time of writing, these are the majority of `.webidl`s.
-
 ### `webidls/enabled/*.webidl`
 
 These are the WebIDL interfaces that we will actually generate bindings for (or
@@ -40,3 +33,12 @@ time in `build.rs`. Here is the whole `src/lib.rs` file:
 ```rust
 {{#include ../../../crates/web-sys/src/lib.rs}}
 ```
+
+### Cargo features
+
+When compiled the crate is almost empty by default, which probably isn't what
+you want! Due to the very large number of APIs, this crate uses features to
+enable portions of its API to reduce compile times. The list of features in
+`Cargo.toml` all correspond to types in the generated functions. Enabling a
+feature enables that type. All methods should indicate what features need to be
+activated to use the method.
diff --git a/guide/src/web-sys/testing.md b/guide/src/web-sys/testing.md
index 411c2200ae9..b7757402d4b 100644
--- a/guide/src/web-sys/testing.md
+++ b/guide/src/web-sys/testing.md
@@ -5,8 +5,7 @@ You can test the `web-sys` crate by running `cargo test` within the
 
 ```sh
 cd wasm-bindgen/crates/web-sys
-cargo test
-cargo test --target wasm32-unknown-unknown
+cargo test --target wasm32-unknown-unknown --all-features
 ```
 
 The Wasm tests all run within a headless browser. See [the `wasm-bindgen-test`