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Whats the point of DOCTYPE?

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夕颜 2020-12-06 17:56

I know that different doctypes are essentially about how compliant the html is, but what difference does it make what doctype you specify? Do browsers handle the same code d

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  • [愿得一人]
    2020-12-06 18:29

    The declaration is not an XHTML tag; it is an instruction to the web browser about what version of the markup language the page is written in.

    The declaration refers to a Document Type Definition (DTD). The DTD specifies the rules for the markup language, so that the browsers render the content correctly.

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  • 忘掉有多难
    2020-12-06 18:31

    The doctype declaration should be the first thing in an HTML document, before the tag.

    It isn't an HTML tag; it's an instruction to the web browser about what version of the markup language the page is written in.

    It's getting simpler with HTML5: <!DOCTYPE html>

    If you don't have that proper doctype, the browser won't know to use HTML5.

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  • 抹茶落季
    2020-12-06 18:32

    Browser Modes

    Back in the past, Browsers implemented CSS to their own rules.
    Only over the years have Browser now adapted the W3C standards.

    To make sure that websites rendered correctly various browsers, web developers had to implement CSS according to the wishes of these browsers. Thus, most websites used CSS in ways that didn’t quite match the specifications.

    Therefore, when standards compliancy became important browser vendors faced a tough choice. Moving closer to the W3C specifications was the way to go, but if they’d just change the CSS implementations to match the standards perfectly, many websites would break to a greater or lesser extent. Existing CSS would start to show odd side effects if it were suddenly interpreted in the correct way.

    So moving closer to standards compliance would cause problems. On the other hand, not moving closer to standards compliance would perpetuate the general confusion of the Browser Wars Era.

    To this end all Browser had to start supporting both modes. Quirks mode for older designs and standard mode for new design.

    Paraphrased from here: Quirks mode and strict mode

    DocTypes

    Choosing which mode to use requires a trigger, and this trigger was found in ’doctype switching’. According to the standards, any (X)HTML document should have a doctype which tells the world at large which flavour of (X)HTML the document is using.

    Taken from here too: Quirks mode and strict mode

    Additonal Resources

    • Document Type Declaration
    • Quirks Mode on Wikipedia
    • Quirks mode and strict mode
    • Internet Explorer box model bug
    • The CSS box model
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  • 粉色の甜心
    2020-12-06 18:37

    From Wikipedia:

    A Document Type Declaration, or DOCTYPE, is an instruction that associates a particular SGML or XML document (for example, a webpage) with a Document Type Definition (DTD) (for example, the formal definition of a particular version of HTML). In the serialized form of the document, it manifests as a short string of markup that conforms to a particular syntax.

    The HTML layout engines in modern web browsers perform DOCTYPE "sniffing" or "switching", wherein the DOCTYPE in a document served as text/html determines a layout mode, such as "quirks mode" or "standards mode". The text/html serialization of HTML5, which is not SGML-based, uses the DOCTYPE only for mode selection. Since web browsers are implemented with special-purpose HTML parsers, rather than general-purpose DTD-based parsers, they don't use DTDs and will never access them even if a URL is provided. The DOCTYPE is retained in HTML5 as a "mostly useless, but required" header only to trigger "standards mode" in common browsers.

    I decided to quote this text because it answers your question better than I would :). It is important that the absence of a DOCTYPE will trigger "quirks mode" in certain browsers.

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  • 孤街浪徒
    2020-12-06 18:37

    It's all about the standards and yes, browsers handles code differently. That means, that all browsers should display the page equally. If no standard is specified, browser will interpret the page as it wants.

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  • 臣服心动
    2020-12-06 18:42

    Because Doctype is the flag to tell how the browser should handle the page.

    For example :

    HTML5 need this doctype<!DOCTYPE html> If you remove this from the page, the any HTML5 capabilities inside your page won't be activated.

    You can read more in http://www.w3.org/QA/Tips/Doctype

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