# HTML Standard FAQ _See also the [WHATWG FAQ](https://whatwg.org/faq)._ ## HTML ### What is HTML? [HTML](https://html.spec.whatwg.org/multipage/) is the core foundational standard being worked on by the WHATWG community. It is continuously maintained and supersedes HTML4, XHTML1, DOM Level 2 HTML, and all previous HTML specifications — addressing many of the shortcomings of those specifications while at the same time enhancing HTML to more adequately cover the needs of web applications. Along with defining the HTML markup language, it also defines many of the core requirements that form the basis of the web runtime. ### What is HTML5? Going forward, the WHATWG is just working on "HTML", without worrying about version numbers. When people talk about "HTML5" in the context of the WHATWG, they usually mean just "the latest work on HTML", not necessarily a specific version. For more details, see the section called "[Is this HTML5?](https://html.spec.whatwg.org/multipage/introduction.html#is-this-html5?)" in the standard. ### How do I validate my pages? Use a [validator](https://whatwg.org/validator/). ### What parts of the standard are stable? The whole standard is more or less stable. There are some parts of it that describe new technologies that have not yet been implemented everywhere, but at this point those additions are only added after the design itself is pretty stable. Such additions must also have the support of two or more implementers, [per our working mode](https://whatwg.org/working-mode#additions). ### Why are there no stable snapshots, or versions, of the standard? In practice, implementations all follow the latest standard anyway, not so-called "finished" snapshots. The problem with following a snapshot is that you end up following something that is _known to be wrong_. That's obviously not the way to get interoperability! This has in fact been a real problem at the W3C, where mistakes are found and fixed in the editors' drafts of specifications, but implementers who aren't fully engaged in the process go and implement obsolete snapshots instead, including those bugs. This has resulted in serious differences between browsers. For more information on this, see the WHATWG FAQ entry [What does "Living Standard" mean?](https://whatwg.org/faq#living-standard). ### Will future browsers have any idea what older HTML documents mean? Browsers do not implement HTML+, HTML2, HTML3.2, HTML4, HTML4.01, etc, as separate versions. They all just have a single implementation that covers all these versions at once. That is what the HTML Standard defines: how to write a browser (or other implementation) that handles _all previous versions of HTML_, as well as all the latest features. One of the main goals of the HTML Standard and the WHATWG effort as a whole is to make it possible for archeologists hundreds of years from now to write a browser and view HTML content, regardless of when it was written. Making sure that we handle all documents is one of our most important goals. Not having versions does not preclude this; indeed it makes it significantly easier. ### How are developers to determine when certain parts of their pages will become invalid? It shouldn't matter if and when old pages become invalid. Validity (more often referred to as document conformance in the WHATWG) is a quality assurance tool to help authors avoid mistakes. We don't make things non-conforming (invalid) for the sake of it, we use conformance as a guide for developers to help them avoid bad practices or mistakes (like typos). So there's not really any need to worry about whether old pages are conforming or not. It's only helpful when you're writing a new page, and it's always most helpful to have the latest advice. It wouldn't be useful to check for conformance against last week's rules, for instance. After all, we fixed mistakes in those rules this week! For more details, see [part of the introduction](https://html.spec.whatwg.org/multipage/introduction.html#conformance-requirements-for-authors) of the standard. ### How can I keep track of changes to the standard? There are a number of ways to track changes to the standard: * The Twitter feed: [@htmlstandard](https://twitter.com/htmlstandard) * The [GitHub commits log](https://github.com/whatwg/html/commits) * The standard is available in the [Git repository](https://github.com/whatwg/html/). You may use any Git client to check out the latest version and use your client's diff tools to compare revisions and see what has been changed. ### What are the various versions of the HTML Standard? The HTML Standard is available in three forms: [single-page](https://html.spec.whatwg.org/) (_very large_), [multi-page](https://html.spec.whatwg.org/multipage/), and the [developer's edition](https://html.spec.whatwg.org/dev/). The W3C used to publish some [forked versions](https://wiki.whatwg.org/wiki/Fork_tracking) of the HTML Standard. They are no longer maintained and now redirect to the HTML Standard. If you spot any others please open an issue on [w3c/whatwg-coord](https://github.com/w3c/whatwg-coord/issues/) so the W3C staff can work to get them redirected. ### How do I know if a particular feature in the standard is ready to use? Here are some sites to help you work out what you can use: * https://caniuse.com/ * https://developer.mozilla.org/ The following sites also have some useful information: * https://html5doctor.com/ * https://diveintohtml5.info/ If you know of any more (or if you have some yourself) then send a pull request to add them to the list! (Or, if you think any of the above have lost usefulness over time, send a pull request removing them and outlining your reasoning.) ### When will HTML5 be finished? The WHATWG is now using a Living Standard development model, so this question is no longer really pertinent. See above, under "[What is HTML5?](#what-is-html5)". The real question is, when can you use new features? For an answer to that question, see "[How do I know if a particular feature in the spec is ready to use?](#how-do-i-know-if-a-particular-feature-in-the-standard-is-ready-to-use)". ### What's this I hear about 2022? Back before the Living Standard development model, we were planning to put the contents of the HTML Standard through the W3C process. This was before we understood the fatal flaws of such a snapshot-based development mode. At the time, the W3C Recommendation label had high standards, such as 100% test coverage of two complete and fully interoperable implementations. In 2008, the editor estimated it would take another 14 years to reach that point, based on comparing it to the amount of work done for HTML4 and other large specifications like CSS2/2.1. Since then, we've realized that much like the [waterfall model](https://en.wikipedia.org/wiki/Waterfall_model) is not a good fit for software development, it is also not a good way of developing standards. These days we keep the HTML Standard continually under development, adding tests as we go and verifying them against implementations, [per our working mode](https://whatwg.org/working-mode). So, the year 2022 is no longer relevant. ### Is design rationale documented? Sort of. Often some record of the rationale for a particular design choice can be found within discussions in the GitHub issue tracker, commit logs, or the mailing-list archive or [Chat archives](https://whatwg.org/chat#logs). Sometimes, there is an explanation in the specification, but doing that everywhere would make the specification huge. For a few cases that someone did take the time document, the information can be found at the following locations: * [Rationale](https://wiki.whatwg.org/wiki/Rationale) — a page that documents some reasons behind decisions in the spec, originally written and maintained by Variable. If anyone wants to help him out, try to find someone via [Chat](https://whatwg.org/chat); we're always looking for more contributors and this is a good place to start. * [Why no namespaces](https://wiki.whatwg.org/wiki/Why_no_namespaces) * [Why no script implements](https://wiki.whatwg.org/wiki/Why_no_script_implements) * [Why not reuse legend](https://wiki.whatwg.org/wiki/Why_not_reuse_legend) or another _mini-header_ element. Also see [HTML feature proposals](#html-feature-proposals). ## HTML syntax issues ### Does HTML finally put an end to the XHTML as `text/html` debate? Yes. Unlike HTML4 and XHTML1, the choice of HTML or "XHTML" is solely dependent upon the choice of the media type, rather than the DOCTYPE. See [HTML vs. XHTML](https://wiki.whatwg.org/wiki/HTML_vs._XHTML) ### What is the DOCTYPE for modern HTML documents? In `text/html` documents: ```html ``` In documents delivered with an XML media type: no DOCTYPE is required and its use is generally unnecessary. However, you may use one if you want (see the following question). Note that the above is well-formed XML. For compatibility with legacy producers designed for outputting HTML, but which are unable to easily output the above DOCTYPE, this alternative legacy-compat version may be used instead. ```html ``` Note that this is _not_ intended for dealing with any compatibility issues with legacy browsers. It is meant for legacy authoring tools only. Excluding the string `"about:legacy-compat"`, the DOCTYPE is case insensitive in `text/html`. In documents delivered with an XML media type, it is case sensitive and must be either of the two variants given above. For this reason, the DOCTYPEs given above are recommended to be used over other case variants, such as `` or ``. These alternatives were chosen because they meet the following criteria: * They trigger standards mode in all current and all relevant legacy browsers. * They are well-formed in XML. * It is possible to output at least one of the alternatives, if not both, with extant markup generators. * They intentionally contain no language version identifier so the DOCTYPE will remain usable for all future revisions of HTML. * The first is short and memorable to encourage its use. * The legacy-compat DOCTYPE is intentionally unattractive and self descriptive of purpose to discourage unnecessary use. ### Under what conditions should a DOCTYPE be used in a document delivered with an XML media type? Generally, the use of a DOCTYPE in a document delivered with an XML media type is unnecessary. However, there are cases where inclusion of a DOCTYPE is a reasonable thing to do: 1. The document is intended to be a polyglot document such that the same text may be treated as either HTML or XML. 2. You wish to declare entity references for use within the document. Note that most browsers only read the internal subset and do not retrieve external entities. (This is not compatible with HTML, and thus not suitable for polyglot documents.) 3. You wish to use a custom DTD for DTD-based validation. But take note of [what's wrong with DTDs](https://about.validator.nu/#faq). Fundamentally, this is an XML issue, and is not specific to HTML documents delivered with an XML media type. ### How are documents from HTML4 and earlier versions parsed? All documents with a `text/html` media type (that is, including those without or with an HTML 2.0, HTML 3.2, HTML4, or XHTML1 DOCTYPE) will be parsed using the same parser algorithm as defined by the HTML spec. This matches what web browsers have done for HTML documents so far and keeps code complexity down. That in turn is good for security, maintainability, and in general keeping the amount of bugs down. The HTML syntax as now defined therefore does not require a per-version parser, and documents with an HTML4 DOCTYPE for example will be parsed as described by the HTML specification. Validators are allowed to have different code paths for previous levels of HTML. ### If there is no DTD, how can I validate my page? With an [HTML validator](https://whatwg.org/validator/) that follows the latest specification. ### What is an "HTML serialization"? The HTML serialization refers to the syntax of an HTML document defined in the HTML specification. The syntax is inspired by the SGML syntax from earlier versions of HTML, bits of XML (e.g. allowing a trailing slash on void elements, `xmlns` attributes), and reality of deployed content on the web. Any document whose media type is determined to be `text/html` is considered to be an HTML serialization and must be parsed using an HTML parser. ### What is an XML (or XHTML) serialization? The XML serialization refers to the syntax defined by XML 1.0 and Namespaces in XML 1.0. A resource that has an XML media type, such as `application/xhtml+xml` or `application/xml`, is an XML document. XML documents whose root element is `` in the HTML namespace are sometimes referred to as "XHTML" documents. ### What media (MIME) type does HTML use? The HTML serialization _must_ be served using the `text/html` media type. The XML serialization _must_ be served using an XML media type, such as `application/xhtml+xml` or `application/xml`. Unlike the situation as of XHTML1, the HTML specification requires that "XHTML" documents not be served with the `text/html` media type. Using the incorrect media type (`text/html`) for a document in the XML serialization will cause the document to be parsed according to parsing requirements for HTML. In other words, it will be treated as what's sometimes called "tag soup". Ensuring the use of an XML media type is the only way to ensure that browsers handle the document as XML. ### Should I close empty elements with `/>` or `>`? Void elements in HTML (e.g. the `
`, `` and `` elements) do not require a trailing slash. e.g. Instead of writing `
`, you only need to write `
`. This is the same as in HTML4. However, due to the widespread attempts to use XHTML1, there are a significant number of pages using the trailing slash. Because of this, the trailing slash syntax has been permitted on void elements in HTML in order to ease migration from XHTML1 back to HTML. The current HTML specification also introduces the ability to embed MathML elements. On elements inside a `math` element, the trailing slash works just like it does in XML; that is, it closes the element. This is only inside that context however; it does not work for normal HTML elements. ### If I'm careful with the syntax I use in my HTML document, can I process it with an XML parser? You have to be _really_ careful for this to work, and it's almost certainly not worth it. You'd be better off just using an HTML-to-XML parser. That way you can just use HTML normally while still using XML pipeline tools. [HTML vs. XHTML](https://wiki.whatwg.org/wiki/HTML_vs._XHTML#Differences_Between_HTML_and_XHTML) has some related guidance. ### What is the namespace declaration? In the XML syntax, you are required to specify the namespace: ```html ``` In `text/html` documents, the `xmlns` attribute is currently allowed on any HTML element, but only if it has the value `http://www.w3.org/1999/xhtml`. It doesn't do anything at all; it is merely allowed for the purpose of easing migration from XHTML1. It is not actually a namespace declaration in HTML, because HTML doesn't support namespaces. See the question "[What about namespaces in HTML?](#what-about-namespaces-in-html)". ### What about namespaces in HTML? HTML is defined in terms of the DOM and during parsing of a `text/html` document, all HTML elements are automatically put in the HTML namespace, `http://www.w3.org/1999/xhtml`. However, unlike the XML serialization, there is no real namespace syntax available in the HTML serialization (see previous question). In other words, you do not need to declare the namespace in your HTML markup, as you do in XHTML. In addition, the HTML syntax provides for a way to embed elements from MathML and SVG. Elements placed inside the container element `math` or `svg` will automatically be put in the MathML namespace or the SVG namespace, respectively, by the parser. Namespace syntax is not required, but again an `xmlns` attribute is allowed if its value is the right namespace. In conclusion, while HTML does not allow the XML namespace syntax, there is a way to embed MathML and SVG and the `xmlns` attribute can be used on any element under the given constraints, in a way that is reasonably compatible on the DOM level. ### How do I specify the character encoding? Regardless of whether documents are delivered as `text/html` or with an XML media type, UTF-8 is the only conformant character encoding. For HTML, it is strongly recommended that you specify the encoding using the HTTP `Content-Type` header. If you are unable to [configure your server](https://www.w3.org/International/articles/http-charset/) to send the correct headers, then you may use the `` element: ```html ``` In addition, the following restrictions apply: * The character encoding name given must be the name of the character encoding used to serialize the file. * The character encoding declaration must be serialized without the use of character references or character escapes of any kind. * The `` element used for this purpose must occur within the first 512 bytes of the file. It is considered good practice for this to be the first child of the `` element so that it is as close to the beginning of the file as possible. Note that this `` element is different from HTML4, though it is compatible with many browsers because of the way encoding detection has been implemented. To ease transition from HTML4 to the current HTML specification, although the former is the recommended syntax, you may also use the following. (This does not apply to documents in the XML syntax): ```html ``` In documents delivered with an XML media type, XML rules for determining the character encoding declaration apply. The `` element is never used for determining the encoding of such documents; for those, you should use either the HTTP `Content-Type` header or the XML declaration to specify the encoding. ```html ``` However, because documents which do not have an XML declaration that explicitly specifies an encoding are processed as UTF-8, it's not necessary for conforming documents to include an XML declaration to specify the encoding. ### What are the differences between HTML and XHTML? See the list of [differences between HTML and XHTML](https://wiki.whatwg.org/wiki/HTML_vs._XHTML#Differences_Between_HTML_and_XHTML) in the wiki. ### What are best practices to be compatible with HTML DOM and XML DOM? Though the intent is that documents delivered with a `text/html` media type and that documents delivered with an XML media type can both produce identical DOMs, there still are some differences between working with an HTML DOM and an XML DOM. Case sensitivity: * Whenever possible, avoid testing `element.tagName` and `node.nodeName` (or do `toLowerCase()` before testing). Namespaces: * Use the namespace-aware version for creating elements: `document.createElementNS(ns, elementName)`. ### Why does the HTML Standard legitimize tag soup? Actually it doesn't. This is a misconception that comes from the confusion between conformance requirements for documents, and the requirements for user agents. Due to the fundamental design principle of supporting existing content, the spec must define how to handle all HTML, regardless of whether documents are conforming or not. Therefore, the spec defines precisely how to handle and recover from erroneous markup, much of which would be considered "tag soup". For example, the spec defines algorithms for dealing with syntax errors such as incorrectly-nested tags, which will ensure that a well-structured DOM tree can be produced. Defining that is essential for achieving interoperability between browsers and reducing the dependence upon browsers needing to reverse engineer each other's parsing behavior. However, the conformance requirements for authors are defined separately from the processing requirements. Just because browsers are required to handle erroneous content, it does not make such markup conforming. For example, user agents are required to support processing of the `` element, but authors must not use the `` element in conforming documents. It is important to make the distinction between the rules that apply to user agents and the rules that apply to authors for producing conforming documents. They are completely orthogonal. ## HTML feature proposals ### HTML should support `href` on any element! The spec allows `` to contain blocks. It doesn't support putting `href=""` on any element, though. Supporting `href` on any element has several problems associated with it that make it difficult to support in HTML. The main reason this isn't in HTML is that browser vendors have reported that implementing it would be extremely complex. Browser vendors get to decide what they implement, and there's no point to us telling them to do something they aren't going to do. In addition: * It isn't backwards compatible with existing browsers. * It adds no new functionality that can't already be achieved using the `a` element and a little script. * It doesn't make sense for all elements, such as interactive elements like `input` and `button`, where the use of href would interfere with their normal function. The only advantage it seems to add is that it reduces typing for authors in some cases, but that is not a strong enough reason to support it in light of the other reasons. Wrapping `` elements around blocks solves most use cases. It doesn't handle making rows in tables into links, though; for those just do something like this instead: ```html ... ``` ### HTML should support list headers! You can give a header to a list using the `
` and `
` elements: ```html
Apples
  • Granny Smith
  • Evil Apple of Knowledge
  • Apple, Inc
``` You can also label a group of lists using a definition list: ```html
Dry:
  • 1c flour
  • 1/4c sugar
  • 1tsp baking soda
Wet:
  • 1 egg
  • 1/2c milk
  • 1tsp vanilla extract
``` These techniques are preferred over adding an `` element as proposed in the old HTML3 draft, mostly because of thorny issues with parsing near `
  • ` elements. ### HTML should support a way for anyone to invent new elements! It does. You can use [custom elements](https://html.spec.whatwg.org/multipage/custom-elements.html) to build your own fully-featured DOM elements. Short of that, there are actually quite a number of ways for people to invent their own extensions to HTML: * Authors can use the `class` attribute to extend elements, effectively creating their own elements, while using the most applicable existing "real" HTML element, so that browsers and other tools that don't know of the extension can still support it somewhat well. This is the tack used by Microformats, for example. * Authors can include data for scripts to process using the `data-*=""` attributes. These are guaranteed to never be touched by browsers, and allow scripts to include data on HTML elements that scripts can then look for and process. * Authors can use the `` mechanism to include page-wide metadata. Names should be registered on the wiki's [MetaExtensions](https://wiki.whatwg.org/wiki/MetaExtensions) page. * Authors can use the `rel=""` mechanism to annotate links with specific meanings. This is also used by Microformats. Names should be registered on the wiki's [RelExtensions](https://wiki.whatwg.org/wiki/RelExtensions) page. * Authors can embed raw data using the `