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fix(html): better explanation for DOCTYPE (#144) 

English is not my native language so feel free to tell me if there is any mistake
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Frédéric Espiau 2018-10-26 01:01:59 +02:00 committed by Yangshun Tay
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@ -14,17 +14,24 @@ Answers to [Front-end Job Interview Questions - HTML Questions](https://github.c
* [Why you would use a `srcset` attribute in an image tag? Explain the process the browser uses when evaluating the content of this attribute.](#why-you-would-use-a-srcset-attribute-in-an-image-tag-explain-the-process-the-browser-uses-when-evaluating-the-content-of-this-attribute)
* [Have you used different HTML templating languages before?](#have-you-used-different-html-templating-languages-before)
### What does a `DOCTYPE` do?
### What does a DOCTYPE do?
`DOCTYPE` is an abbreviation for “document type”. It is a declaration used in HTML to distinguish between standards mode and [quirks mode](https://quirks.spec.whatwg.org/#history). Its presence tells the browser to render the web page in standards mode.
**DOCTYPE** is an abbreviation for **DOCument TYPE**.
A DOCTYPE is always associated to a **DTD** - for **Document Type Definition**.
Moral of the story - just add `<!DOCTYPE html>` at the start of your page.
A DTD defines how documents of a certain type should be structured (i.e. a `button` can contain a `span` but not a `div`), whereas a DOCTYPE declares what DTD a document *supposedly* respects (i.e. this document respects the HTML DTD).
For webpages, the DOCTYPE declation is required. It is used to tell user agents what version of the HTML specifications your document respects.
Once a user agent has recognized a correct DOCTYPE, it will trigger the **no-quirks mode** matching this DOCTYPE for reading the document.
If a user agent doesn't recognize a correct DOCTYPE, it will trigger the **quirks mode**.
The DOCTYPE declaration for the HTML5 standards is `<!DOCTYPE html>`.
###### References
* https://stackoverflow.com/questions/7695044/what-does-doctype-html-do
* https://www.w3.org/QA/Tips/Doctype
* https://quirks.spec.whatwg.org/#history
* https://html.spec.whatwg.org/multipage/syntax.html#the-doctype
* https://html.spec.whatwg.org/multipage/xhtml.html
* https://quirks.spec.whatwg.org/
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