Features in the HTML spec that are known to have less than two implementations

[sideshowbarker]

Below is the list of features in the HTML spec that — per current https://github.com/mdn/browser-compat-data/ (BCD) data — are known to have less than two implementations.

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the-offscreencanvas-interface API/OffscreenCanvas

• dom-offscreencanvas API/OffscreenCanvas/OffscreenCanvas
• dom-offscreencanvas-converttoblob API/OffscreenCanvas/convertToBlob
• dom-offscreencanvas-getcontext API/OffscreenCanvas/getContext
• dom-offscreencanvas-height API/OffscreenCanvas/height
• dom-offscreencanvas-transfertoimagebitmap API/OffscreenCanvas/transferToImageBitmap
• dom-offscreencanvas-width API/OffscreenCanvas/width
• offscreencontext-commit API/WebGLRenderingContext/commit

rel-alternate CSS/Alternative_style_sheets

• attr-style-title CSS/Alternative_style_sheets
• attr-meta-http-equiv-default-style CSS/Alternative_style_sheets
• link-type-stylesheet CSS/Alternative_style_sheets

• dom-media-srcobject API/HTMLMediaElement/srcObject [partial; can only set MediaStream]
• dom-context-2d-scrollpathintoview API/CanvasRenderingContext2D/scrollPathIntoView
• autocapitalization HTML/Global_attributes/autocapitalize
• dom-sharedworkerglobalscope-close API/SharedWorkerGlobalScope/close
• dndevents API/Document/dragexit_event
• handler-oncancel API/GlobalEventHandlers/oncancel
• dom-accesskeylabel API/HTMLElement/accessKeyLabel
• selector-ltr CSS/:dir
• meta-theme-color HTML/Element/meta/name/theme-color
• link-type-modulepreload HTML/Link_types/modulepreload
• link-type-preload HTML/Link_types/preload
• link-type-prerender HTML/Link_types/prerender
• event-cancel API/HTMLDialogElement/cancel_event

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The following are false positives; the BCD data for them isn’t accurate and needs to be updated.

audiotrack API/AudioTrack [mdn/browser-compat-data/pull/6224]

• dom-audiotrack-enabled API/AudioTrack/enabled
• dom-audiotrack-id API/AudioTrack/id
• dom-audiotrack-kind API/AudioTrack/kind
• dom-audiotrack-label API/AudioTrack/label
• dom-audiotrack-language API/AudioTrack/language

videotrack API/VideoTrack [mdn/browser-compat-data/pull/6224]

• dom-videotrack-id API/VideoTrack/id
• dom-videotrack-kind API/VideoTrack/kind
• dom-videotrack-label API/VideoTrack/label
• dom-videotrack-language API/VideoTrack/language
• dom-videotrack-selected API/VideoTrack/selected

• event-pagehide API/Window/pagehide_event [updating compat data for pageshow and pagehide events mdn/browser-compat-data#6187]
• event-pageshow API/Window/pageshow_event [updating compat data for pageshow and pagehide events mdn/browser-compat-data#6187]
• dom-img-decode API/SVGImageElement/decode
• image-decoding-hint API/SVGImageElement/decoding
• handler-onabort API/GlobalEventHandlers/onabort
• dom-datatransfer API/DataTransfer/DataTransfer
• event-media-addtrack API/TextTrackList/addTrack_event
• event-media-change API/TextTrackList/change_event
• event-media-removetrack API/TextTrackList/removeTrack_event
• event-message API/Window/message_event
• handler-window-onmessage API/WindowEventHandlers/onmessage
• texttrackcue API/TextTrackCue
• closeevent API/CloseEvent/CloseEvent
• the-trackevent-interface API/TrackEvent
• dom-trackevent-track API/TrackEvent/track
• dom-navigator-plugins API/NavigatorPlugins/plugins
• dom-navigator-mimetypes API/NavigatorPlugins/mimeTypes
• dom-navigator-javaenabled API/NavigatorPlugins/javaEnabled
• the-menu-element HTML/Element/menu
• event-close API/HTMLDialogElement/close_event