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What is the purpose of the HTML doctype declaration?

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This is the HTML doctype declaration, and it serves an important purpose for web applications. In this article, you will learn what the doctype declaration is, why it is needed, how it affects the browser's rendering mode, and how to use it correctly.

本文章的要点总结

Define the browser's HTML mode:

The doctype declaration ensures the browser uses the correct HTML version. This consistency helps your web page render accurately across different browsers.### *Prevent quirks mode issues:Including a proper doctype prevents browsers from entering quirks mode. This avoids rendering problems and keeps your web application functioning smoothly.

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Guilherme Siquinelli

Arquiteto Web, co-fundador da…
Mumtaz Haqiqy

Software Developer | Fullstack | Front…

1 What is the doctype declaration?

The doctype declaration is a way of telling the browser what version of HTML the web page is using. HTML stands for HyperText Markup Language, and it is the standard language for creating web pages. HTML has evolved over the years, and different versions have different features and syntax rules. The doctype declaration helps the browser to interpret the HTML code correctly and display the web page as intended.

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Guilherme Siquinelli

Arquiteto Web, co-fundador da comunidade DevParaná e curioso pelo Universo
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<!DOCTYPE html> DOCTYPEs s?o necessários por motivos legados. Caso seja omitido, o navegador tende a usar um modo de renderiza??o diferente, incompatível com algumas especifica??es. Ent?o, incluir o DOCTYPE no inicio do documento é um pedido para que o navegador fa?a um esfor?o para seguir as especifica??es relevantes contidas no documento HTML.

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Mumtaz Haqiqy

Software Developer | Fullstack | Front Back End | MsSQL | Postgres | Dotnet | C# | Python | Azure dev-ops
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Doctype declaration is an instruction about what version of HTML the page is written to the browser, this will ensure that all different browser parse the same way to the page.

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Ebenezer Igbinoba

Senior Frontend Engineer | Expert in React, Next.js, Vue.js, Typescript, Automated Testing | Mentor & Team Leader | Passionate about Driving Business Growth through Innovative Web Solutions
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Doctype HTML is a declaration that tells the browser what version of HTML the document is written in. This declaration appears as the very first line in an HTML file.

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Chaitali Khangar

Technical Architect at Sedin Technologies - RailsFactory | Ruby on Rails | Passionate About Mentoring and Teaching Programming Skills | Golang | Angular JS
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The primary purpose of the DOCTYPE declaration is to inform browsers about the version of the markup language in which the document is written. This helps browsers to render the document correctly by applying the appropriate parsing rules and rendering modes. It also helps ensure consistency in the way different browsers interpret and display the document.

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Alex Samier

.NET Architect, SOA, Kubernetes
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Although it looks like one, the declaration is actually not an HTML tag. It is an "information" to the browser about what document type to expect. Nowadays with HTML5, it is very simple (<!DOCTYPE html>) but before it was a bit more tricky because it had to refer to a Document Type Definition (DTD)

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2 Why is the doctype declaration needed?

The doctype declaration is needed because browsers have to deal with web pages that use different versions of HTML, or even invalid or malformed HTML. Without the doctype declaration, the browser would have to guess what version of HTML the web page is using, and it might render it in a way that is inconsistent, unpredictable, or incompatible with the web application's functionality. For example, some HTML elements or attributes might be ignored, some CSS styles might not be applied, or some JavaScript features might not work.

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Chisom Okoye

Frontend Engineer - Web at Kuda
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The Doctype declaration is an instruction to the web browser about what version of HTML the page is written in. and It controls whether the browsers uses "standards" or "quirks" mode to render the document. If the doctype is not declare it forces the document to render in quirks, thereby messing up how your document would appear on the screen.

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Krish Maharjan

Python | Microservices | Django | Docker | Kubernetes
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HTML doctype is is similar to providing a universal translator, to further clarify it sets the rules for how browsers interpret a web page. It makes sure that it is interpreted and shown correctly in all browsers. The code may have problems with interpretation in it's absence.

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Joel Bello

Frontend Developer
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Even though it's easier now, declaring the DOCTYPE ensures older browsers understand your code correctly. It's like speaking a clear language to avoid misunderstandings

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Veena P D

Freelance Developer ?? | Guest Speaker ?? | Trainer | Mentoring Developers for Success | Website & Mobile Apps Expert ?? | Transforming Ideas into High-Quality Solutions ??
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The doctype is required because it helps in rendering the correct version of HTML that the web app is using. Else few of the elements might not display properly. And alignment might look weird. So basically applications might not load as expected.

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Mohamed Mohy

Software Engineer at Agoda
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If we define the declaration as letting the browser know what language we are speaking, the importance of that is allowing the browser to grab the appropriate dictionary to understand what we want.

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3 How does the doctype declaration affect the browser's rendering mode?

The doctype declaration affects the browser's rendering mode, which is the way the browser handles the HTML code and displays the web page. There are two main rendering modes: standards mode and quirks mode. Standards mode is the mode where the browser follows the official specifications of HTML and CSS, and tries to render the web page as accurately and consistently as possible. Quirks mode is the mode where the browser emulates the behavior of older browsers, and tries to accommodate the web pages that use outdated or invalid HTML. Quirks mode can cause many problems for modern web applications, such as layout issues, compatibility issues, or performance issues.

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Sahil Hirapara

Business Development Manager @ UPSQODE
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A valid doctype declaration triggers standards mode, which aims for a more consistent and standards-compliant rendering of the page. Without a doctype declaration or with an invalid one, browsers may revert to "quirks mode," which can lead to unexpected rendering behavior based on older compatibility practices.

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Wolfgang Pommier

Consultant IT Freelance
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Le mode standard et le mode quirks, ne pas traduire en "bizarreries" qui ne se dit pas en fran?ais. C'est le terme Quirks qui est couramment utilisé.

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Ashish Satpute

Vice President at JPMorganChase
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The Document Type Declaration (DOCTYPE) in HTML, like <!DOCTYPE html>, determines the browser's rendering mode. With a valid DOCTYPE, it enters "standards mode," ensuring consistent rendering based on HTML specifications. Without or with an invalid DOCTYPE, it defaults to "quirks mode," attempting older, non-standardized rendering. Including a correct DOCTYPE is crucial for a predictable and uniform display across browsers.

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Konstantine V.

Operations Manager @ Triple Helix
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Specifying doctype triggers standards mode. When a web browser sees the doctype declaration, it knows to render the document in standards mode. Standards mode is a more strict rendering mode that ensures that the document is displayed correctly across different browsers. It also prevents the browser from entering quirks mode. Quirks mode is a legacy rendering mode that is used to support older browsers that do not understand the latest HTML standards. Quirks mode can cause documents to be displayed incorrectly.

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Joel Bello

Frontend Developer
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It promotes best practices and cleaner code, this mode ensures the browser follows the latest web standards, leading to more consistent and predictable rendering across different browsers.

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4 How to use the doctype declaration correctly?

The doctype declaration should be the first line of the HTML document, before the <html> tag. The doctype declaration should match the version of HTML that the web page is using. The most common and recommended doctype declaration for web applications is: <!DOCTYPE html> This doctype declaration tells the browser to use standards mode and to treat the web page as HTML5, which is the latest and most widely supported version of HTML. HTML5 is designed to be backward compatible with older versions of HTML, so it can handle most web pages that use previous versions as well.

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Stephen Kuforiji

Web Software Engineer
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When we build websites using popular tools like React or Vue, they automatically add the doctype for us. This small step makes sure our websites work well and follow the basic rules of the web. It's a neat trick that helps even if we're not thinking about it. This is especially handy because it keeps our web projects aligned with important web standards right from the start

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Dhaval Patel

Founder & CEO at CodeSynergiX | Service Provider | Freelancer | Full Stack Developer | Team Leader | Angular | React | Node | Laravel | Symfony | CodeIgniter | CakePhp | Drupal | Bootstrap | Material Design
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To use the Document Type Declaration (DOCTYPE) correctly, include it at the beginning of your HTML or XML document. The correct DOCTYPE depends on the version you're using. For HTML5, use <!DOCTYPE html>. Place it before the <html> tag to instruct the browser on rendering rules. The DOCTYPE ensures standards compliance, consistent rendering, and compatibility across browsers. Choose the appropriate declaration for your document version and position it strategically to influence the browser's rendering mode, promoting a stable and predictable user experience.

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Konstantine V.

Operations Manager @ Triple Helix
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The doctype declaration must be the very first thing in your HTML document, before any other tags. The doctype declaration is not case-sensitive so there's no worries if it's in all caps. There are different doctype declarations for different versions of HTML, ie HTML5, HTML 4.01, etc..

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Joel Bello

Frontend Developer
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<!DOCTYPE html> <html> <head> <title>Your Page Title</title> </head> <body> </body> </html> - Always include the DOCTYPE declaration in your HTML5 documents. - Use the simple <!DOCTYPE html> syntax. - Place it at the very top of your file. - No additional attributes or URLs are necessary.

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Shoaib Ahmad

MERN stack || React JS || Node JS || ExpressJS || MongoDB || Redux ||
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To use the doctype declaration correctly in HTML, simply include it at the very beginning of your HTML document, before any other HTML tags. For HTML5, use the following declaration: <!DOCTYPE html> <html> <head>  </head> <body>  </body> </html>

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5 What are the benefits of using the doctype declaration?

Using the doctype declaration has numerous advantages for web applications, such as ensuring the browser renders the web page in standards mode. This improves the consistency, compatibility, and quality of the web page across different browsers and devices. Moreover, it enables the use of HTML5 features, such as semantic elements, multimedia elements, form validation, accessibility, and interactivity. This enhances the functionality and user experience of the web application. Additionally, it helps to avoid errors and bugs that may occur due to invalid or outdated HTML code, which reduces development and maintenance costs. Lastly, it improves the SEO (Search Engine Optimization) of the web page, increasing the visibility and ranking of the web application on search engines.

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Shoaib Ahmad

MERN stack || React JS || Node JS || ExpressJS || MongoDB || Redux ||
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using the doctype declaration ensures proper rendering, compatibility, standardization, and facilitates validation for your HTML documents.

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Dech Ganapathy Kechamada

Senior Full Stack Developer (Angular + NodeJS + MongoDB ) | Agile Coach | Scrum Master | Microservice Architecture
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Doc type declaration ensured that all web browsers understand the web page in the same way as intended by the web developer. All the features related the version of the html in the web page will work as expected.

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SOUMICK SINHA

Lead Full Stack Developer @Cisco ? Tech Enthusiast ? AWS Certified Cloud Practitioner
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Doctype ensures cross-browser consistency, modern feature access, and standards-complaint validation, essential for pro web development.

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Dhaval Patel

Founder & CEO at CodeSynergiX | Service Provider | Freelancer | Full Stack Developer | Team Leader | Angular | React | Node | Laravel | Symfony | CodeIgniter | CakePhp | Drupal | Bootstrap | Material Design
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The Document Type Declaration (DOCTYPE) offers numerous benefits in web development. It ensures rendering consistency across browsers and devices, promoting standardized interpretation of HTML or XML. By specifying the document type, developers maintain compatibility and control over layout, enhancing the user experience. DOCTYPE facilitates validation, improving code quality, and supporting accessibility for users with disabilities. Additionally, it contributes to search engine optimization, ensuring proper indexing. Lastly, the declaration aids in future-proofing by providing clarity on the document's intended structure and version, facilitating maintenance and updates over time.

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Nagesh Kulkarni

Dotnet FullStack | Lead | Web Development | Azure DevOps | SQL Server | PRINCE II
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To avoid misrepresentation of the web page , it is essential to tell the browser on what version the document is written in. It ensures consistency across browsers

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6 What are the common mistakes to avoid with the doctype declaration?

When it comes to the doctype declaration, there are some common mistakes to avoid. Omitting the doctype declaration can cause the browser to use quirks mode and render the web page incorrectly. Additionally, using an incorrect or obsolete doctype declaration may lead to the browser using a different version of HTML or a different rendering mode than expected. Furthermore, adding extra spaces or characters before or after the doctype declaration might confuse the browser or invalidate the HTML document. Lastly, using a case-sensitive or XHTML doctype declaration might not work on some browsers or platforms.

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Ashwin Sathian

Lead Engineer | SaaS Product Specialist | Driving Innovation with Angular, Node.js, MongoDB, & Cloud Technologies
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Think of the HTML doctype declaration like a compass for your webpage. It guides the browser on how to correctly interpret the content. But, just like a compass, if it’s not set right, you might end up in uncharted waters. Always use the latest HTML5 doctype (`<!DOCTYPE html>`) to keep your pages sailing smoothly. Place it at the very top, without any extra spaces or characters, to avoid the murky waters of quirks mode. Remember, even a tiny mistake here can lead your page into a storm of display issues. It's the first, crucial step in charting your webpage's journey.

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Neila Ben Lakhal

Assistant Professor of Computer Science | Web services, software architecture
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A doctype declaration is essential for the browser to interpret correctly the HTML code. It must be the first line in an HTML document, no other character or space to be included before it. Furthermore, it is the only doctype way declaration to be used from HTML5 onwards.

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Shoaib Ahmad

MERN stack || React JS || Node JS || ExpressJS || MongoDB || Redux ||
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Common mistakes with the doctype in HTML, in simple terms: 1. **Missing Declaration:** Forgetting to include `<!DOCTYPE html>` at the beginning of your HTML document can lead to unpredictable rendering issues. 2. **Incorrect Placement:** Place the doctype at the very beginning, before any HTML tags. Putting it elsewhere may cause browsers to interpret your document incorrectly. 3. **Wrong Version:** Use the correct doctype for the HTML version you're using (e.g., HTML5). Using an outdated or incorrect doctype can result in compatibility problems. Remember: Include `<!DOCTYPE html>` first, at the top of your HTML, to ensure smooth rendering and compatibility.

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Attila Kobza

Digital Director at Mediator - The Full Service Agency
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Including Comments or Elements Before the DOCTYPE: Placing comments, HTML tags, or any other content before the DOCTYPE declaration can cause some browsers to switch to quirks mode, leading to unexpected rendering issues. Incorrect Placement: The DOCTYPE declaration must be the very first line of your HTML document, before the <html> tag. If it's placed incorrectly, browsers might not render the page as expected. Omitting the DOCTYPE Declaration: Not including a DOCTYPE declaration at the top of your HTML document is a significant mistake. Without it, the browser may render the page in "quirks mode," leading to inconsistent behaviors and styling across different browsers.

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Praful Kamble

Founder & Director @ Wiriya Technology Pvt Ltd. | ICT Consultant | Adobe Certified Professional - Adobe Commerce Business Practitioner | PRINCE 2? Practitioner & ITIL-F Certified
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The doctype declaration is an essential part of an HTML document as it defines the version of HTML being used. 1. Missing or Incorrect Doctype Declaration: Always include a doctype declaration at the beginning of an HTML document. 2. Incorrect Syntax: Make sure there are no typos, extra spaces, or characters before the doctype declaration. 3. Using Outdated or Deprecated Doctype: Using an outdated or deprecated doctype can result in compatibility issues and incorrect rendering. 4. Incorrectly Specifying Doctype: Ensure that the doctype specified accurately reflects the version of HTML you're using.

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7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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Dmitry Vishnevetsky

10K+ Followers | Front End Expert | Founder & CEO @ Mega Profit Apps
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In the lively town of Browserville, web developer Alex forgot to include `<!DOCTYPE html>` while creating a website for the Town Fair. The absence caused browsers to interpret the code differently, resulting in a mishmash of styles. Chaos ensued until a wise coder advised Alex to add the doctype, bringing order back to Browserville and teaching everyone the importance of proper declarations. The Town Fair was a success, and the tale of Browserville became a cautionary lesson for web developers.

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Hilal Rauf

Senior Software Engineer | PHP | Laravel | CodeIgniter | MySQL | AWS | JQuery | JS | API | Rest API | Socket.io | WebSocket | Redis
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Well doctype is not eventually a html tag but it's kind of special instruction, which tells web browser that in which HTML version the page is written in. This must be at top or at the very beginning of a html page. Syntax: For HTML 5- <!DOCTYPE html> Which was more complex in HTML 4.01 as DOCTYPE uses document type definition (DTD)

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Daniel Barroso
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Além do <!DOCTYPE html> que é a mais usada na web, há diversas outras linguagens de marca??o disponíveis como por exemplo XHTML, MathML e SVG.

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What is the purpose of the HTML doctype declaration?

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1 What is the doctype declaration?

2 Why is the doctype declaration needed?

3 How does the doctype declaration affect the browser's rendering mode?

4 How to use the doctype declaration correctly?

5 What are the benefits of using the doctype declaration?

6 What are the common mistakes to avoid with the doctype declaration?

7 Here’s what else to consider

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What is the purpose of the HTML doctype declaration?

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1 What is the doctype declaration?

2 Why is the doctype declaration needed?

3 How does the doctype declaration affect the browser's rendering mode?

4 How to use the doctype declaration correctly?

5 What are the benefits of using the doctype declaration?

6 What are the common mistakes to avoid with the doctype declaration?

7 Here’s what else to consider

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