Document interfaces

document.md

Document interfaces

This is the state of Document, HTMLDocument, SVGDocument and XMLDocument interfaces on the web platform as of September 2016. Main spec issues:

• Un-merge Document and HTMLDocument
• Figure out what to do with XMLDocument

See the timeline for history and tests for current behavior.

Paths to interop

These are the options in terms of which document interfaces are concrete:

HTMLDocument and XMLDocument

Document becomes an abstract interface like Node or CharacterData. The Document constructor is removed.

Changes:

• Chromium: None/trivial.
• Edge: Make existing Document instances XMLDocument instead.
• Gecko: Remove the Document constructor. Make existing SVGDocument instances XMLDocument instead.
• WebKit: Remove the Document constructor.

Document, HTMLDocument and XMLDocument

Like above, but the Document constructor remains, and is the only way to create a Document instance. When both Document and XMLDocument are concrete and represent the same thing, this is the least inconsistent state possible. It would be an odd API to avoid.

Changes:

• Chromium: Implement the Document constructor.
• Edge: Implement the Document constructor. Make existing Document instances XMLDocument instead.
• Gecko: Make existing SVGDocument instances XMLDocument instead.
• WebKit: None/trivial.

Document and HTMLDocument

XMLDocument is made an alias of Document.

Changes:

• Chromium: Make XMLDocument an alias of Document again.
• Edge: Make XMLDocument an alias of Document.
• Gecko: Make XMLDocument an alias of Document, dropping async and load(). Make existing SVGDocument instances Document instead.
• WebKit: Make XMLDocument an alias of Document again.

Just Document

Like above, but also attempt making HTMLDocument an alias of Document.

Compat constraints

Is HTMLDocument needed?

Maybe.

The risk of making HTMLDocument an alias of Document is for documents that are currently not instanceof HTMLDocument. The string "instanceof HTMLDocument" is common in HTTP Archive, and it would require in-depth analysis to judge the risk.

Is XMLDocument needed?

Maybe.

Gecko has async and load() on XMLDocument. They were originally on Document, which broke stuff. A usecounter in Gecko could help.

For WebKit-identifying engines it is likely still Web compatible to make XMLDocument an alias of Document, as that was done from 2006 to 2016 in WebKit and up to 2014 in Chromium.

What about Sarissa?

A problem with virginamerica.com resulted in a lot of changes in 2011. The problem was in the Sarissa library, in GlobalScriptFile_08232011.js (pretty-printed) on virginamerica.com.

The spec bug was resolved by adding [LenientThis] to onreadystatechange, so that XMLDocument.prototype.onreadystatechange = null silently does nothing.

Note that Sarissa merely replaced XMLDocument.prototype.load and internally used the original method. All non-IE browsers get this code path, so it's only if load() is called by some other code that it would break, which is the case without Sarissa as well.

Is SVGDocument needed?

Probably not.

Is the Document constructor needed?

Maybe. Gecko and WebKit engineers are skeptical about removing it.

What should be on Document vs. HTMLDocument?

This probably does not matter for compat, because Edge has everything on Document and the other engines still have a variety of things on HTMLDocument. "As long as we have interop, it doesn't really matter where the properties are, so take the path of least resistance."

Timeline

IE6 (tested) and possibly earlier (not tested) could create documents using MSXML which supported async and load().

2000

• Gecko: Added support for loading an XML document "out of band" from script and manipulating it via dom interfaces.

2001

• DOM Level 3 Content Models and Load and Save: document.load and friends first appear.
• Gecko: Simple Javascript doesn't work
• Removing the method load() from HTML documents, implement it only on XML documents since the name 'load' blocks existing global functions named 'load' from being called from event handlers in the document (since document.load is found before window.load in the scope of event handlers). HTMLDocument.load and XULDocument.load were never implemented any way.

2003

• DOM Level 3 Load and Save: document.load and friends become DOMParser.

2006

• WebKit: Add constructors for DocumentFragment, HTMLElement, HTMLDocument and XMLDocument. XMLDocument is just an alias for the Document constructor (Note: the HTMLElement and HTMLDocument constructors are now gone)
• WebKit: Implement XMLDocument.load (never happened)

2010

• Gecko: Deprecate DOM3 Load (XMLDocument.load) ("Use of document.load() is deprecated. To upgrade your code, use the DOM XMLHttpRequest object. For more help https://developer.mozilla.org/en/XMLHttpRequest")

2011

• Gecko: Virgin America website won't load correctly : Illegal operation on WrappedNative prototype object due to setting XMLDocument.prototype.onreadystatechange
• Allow the onreadystatechange getter/setter on Document.prototype to not throw even if its |this| is bogus
• HTML: Should XMLDocument be standardized?
• Make HTMLDocument === Document + fix + tweak
• Make document.prototype.onreadystatechange not throw, for compat reasons
• Move XMLDocumentLoader.load to XMLDocument.

2012

• SVG: SVGDocument interface (alias to Document?) ("this is the direction HTML is going")
• Make SVGDocument into an alias for document

2013

• Firefox 20 is released with a Document constructor.
• IE11 is released with separate HTMLDocument and XMLDocument interfaces, both empty. Earlier versions of IE had only a Document interface, but could create different kinds of documents using MSXML, see beginning of timeline.

2014

• Chromium: Implement XMLDocument interface
• XMLHttpRequest.responseXML objects and DOMParser.parseFromString objects does not inherit from the same class since Chrome 34 Beta
• WebKit: Document should be constructable
• Gecko: Document() constructor should return Document object (not XMLDocument)

2015

• SVG: window.SVGDocument alias is probably not needed for web compat
• Remove requirement for SVGDocument property on the Document interface object

2016

• WebKit: An XMLDocument interface should be exposed on the global Window object
• DOM: Un-merge Document and HTMLDocument
• HTML: Remove XMLDocument.prototype.load
• DOM: Figure out what to do with XMLDocument
• HTML: Add back XMLDocument.prototype.load in Gecko compatibility mode
• DOM: Clarify that new Document creates a document of type "html", not "xml"
• WebKit: Drop SVGDocument as per the SVG2 specification (Note: leaves SVGDocument alias)
• Gecko: Remove SVGDocument

Tests

• What type of document is used in various contexts?
• What's on the protoypes?

Note: XSLT was not tested.

Chrome 53 on Windows 10

API	Interface
createDocument	XMLDocument
createDocument (xhtml)	XMLDocument
createDocument (svg)	XMLDocument
createHTMLDocument	HTMLDocument
iframe (html)	HTMLDocument
iframe (xhtml)	XMLDocument
iframe (svg)	XMLDocument
iframe (xml)	XMLDocument
XHR (html)	HTMLDocument
XHR (xhtml)	XMLDocument
XHR (svg)	XMLDocument
XHR (xml)	XMLDocument
DOMParser (html)	HTMLDocument
DOMParser (xhtml)	XMLDocument
DOMParser (svg)	XMLDocument
DOMParser (xml)	XMLDocument
DOMParser (invalid xml)	XMLDocument

Interface	Prototype
HTMLDocument	alinkColor, all, bgColor, captureEvents, clear, constructor, fgColor, linkColor, releaseEvents, vlinkColor
XMLDocument	constructor

Edge 14 on Windows 10

API	Interface
createDocument	XMLDocument
createDocument (xhtml)	XMLDocument
createDocument (svg)	XMLDocument
createHTMLDocument	HTMLDocument
iframe (html)	HTMLDocument
iframe (xhtml)	Document
iframe (svg)	Document
iframe (xml)	Document
XHR (html)	HTMLDocument
XHR (xhtml)	XMLDocument
XHR (svg)	XMLDocument
XHR (xml)	XMLDocument
DOMParser (html)	HTMLDocument
DOMParser (xhtml)	XMLDocument
DOMParser (svg)	XMLDocument
DOMParser (xml)	XMLDocument
DOMParser (invalid xml)	Document

Interface	Prototype
HTMLDocument	constructor
XMLDocument	constructor

Firefox 48 on Windows 10

API	Interface
createDocument	XMLDocument
createDocument (xhtml)	HTMLDocument
createDocument (svg)	SVGDocument
createHTMLDocument	HTMLDocument
iframe (html)	HTMLDocument
iframe (xhtml)	HTMLDocument
iframe (svg)	SVGDocument
iframe (xml)	XMLDocument
XHR (html)	HTMLDocument
XHR (xhtml)	XMLDocument
XHR (svg)	XMLDocument
XHR (xml)	XMLDocument
DOMParser (html)	HTMLDocument
DOMParser (xhtml)	XMLDocument
DOMParser (svg)	SVGDocument
DOMParser (xml)	XMLDocument
DOMParser (invalid xml)	XMLDocument

Interface	Prototype
HTMLDocument	alinkColor, all, anchors, applets, bgColor, body, captureEvents, clear, close, constructor, cookie, designMode, domain, embeds, execCommand, fgColor, forms, getElementsByName, getItems, getSelection, head, images, linkColor, links, open, plugins, queryCommandEnabled, queryCommandIndeterm, queryCommandState, queryCommandSupported, queryCommandValue, releaseEvents, scripts, vlinkColor, write, writeln
SVGDocument	constructor, domain, rootElement
XMLDocument	async, constructor, load

Safari 10 on macOS Sierra

API	Interface
createDocument	XMLDocument
createDocument (xhtml)	XMLDocument
createDocument (svg)	SVGDocument
createHTMLDocument	HTMLDocument
iframe (html)	HTMLDocument
iframe (xhtml)	XMLDocument
iframe (svg)	SVGDocument
iframe (xml)	XMLDocument
XHR (html)	HTMLDocument
XHR (xhtml)	XMLDocument
XHR (svg)	XMLDocument
XHR (xml)	XMLDocument
DOMParser (html)	HTMLDocument
DOMParser (xhtml)	XMLDocument
DOMParser (svg)	SVGDocument
DOMParser (xml)	XMLDocument
DOMParser (invalid xml)	XMLDocument

Interface	Prototype
HTMLDocument	alinkColor, all, bgColor, captureEvents, clear, close, compatMode, constructor, designMode, dir, embeds, fgColor, linkColor, open, plugins, releaseEvents, scripts, vlinkColor, write, writeln
SVGDocument	constructor, createEvent, rootElement
XMLDocument	constructor

Note: SVGDocument was made an alias of Document in WebKit, so the results will change in a coming release.

Chrome 33 on Windows 8.1 / Safari 9.1 on OS X El Capitan

In 2006, WebKit added XMLDocument as an alias of Document. Chromium and WebKit got real XMLDocument interfaces inheriting from Document in 2014 and 2016 respectively. Before those changes, Chrome and Safari had a shared behavior, which is likely still web compatible for at least WebKit-identifying engines:

API	Interface
createDocument	Document
createDocument (xhtml)	Document
createDocument (svg)	SVGDocument
createHTMLDocument	HTMLDocument
iframe (html)	HTMLDocument
iframe (xhtml)	Document
iframe (svg)	SVGDocument
iframe (xml)	Document
XHR (html)	HTMLDocument
XHR (xhtml)	Document
XHR (svg)	Document
XHR (xml)	Document
DOMParser (html)	HTMLDocument
DOMParser (xhtml)	Document
DOMParser (svg)	SVGDocument
DOMParser (xml)	Document
DOMParser (invalid xml)	Document

Union of behaviors

API	Interface
createDocument	Document or XMLDocument
createDocument (xhtml)	Document, HTMLDocument or XMLDocument
createDocument (svg)	SVGDocument or XMLDocument
createHTMLDocument	HTMLDocument
iframe (html)	HTMLDocument
iframe (xhtml)	Document, HTMLDocument or XMLDocument
iframe (svg)	Document, SVGDocument or XMLDocument
iframe (xml)	Document or XMLDocument
XHR (html)	HTMLDocument
XHR (xhtml)	Document or XMLDocument
XHR (svg)	Document or SVGDocument
XHR (xml)	Document or XMLDocument
DOMParser (html)	HTMLDocument
DOMParser (xhtml)	Document or XMLDocument
DOMParser (svg)	SVGDocument or XMLDocument
DOMParser (xml)	Document or XMLDocument
DOMParser (invalid xml)	Document or XMLDocument

Excluding Chrome 33 on Windows 8.1 / Safari 9.1 on OS X El Capitan

API	Interface
createDocument	XMLDocument
createDocument (xhtml)	HTMLDocument or XMLDocument
createDocument (svg)	SVGDocument or XMLDocument
createHTMLDocument	HTMLDocument
iframe (html)	HTMLDocument
iframe (xhtml)	Document, HTMLDocument or XMLDocument
iframe (svg)	Document, SVGDocument or XMLDocument
iframe (xml)	Document or XMLDocument
XHR (html)	HTMLDocument
XHR (xhtml)	Document or XMLDocument
XHR (svg)	Document or SVGDocument
XHR (xml)	Document or XMLDocument
DOMParser (html)	HTMLDocument
DOMParser (xhtml)	XMLDocument
DOMParser (svg)	SVGDocument or XMLDocument
DOMParser (xml)	XMLDocument
DOMParser (invalid xml)	Document or XMLDocument

2005:

• Opera 8.01 supports DOM 3 Load and Save

2007:

• Opera 9.5 Beta 1 drops Document.async and Document.load

http://www.opera.com/docs/changelogs/mac/801/
http://www.opera.com/docs/changelogs/windows/950b1/