What is DOCTYPE and why do I want to use it?
What are the different DOCTYPEs I can use?
What is the difference between standards and quirks mode, and what are some quirks I may run into with differently set DOCTYPEs?
Lastly, what is the proper DOCTYPE that I should be using?
Basically, the DOCTYPE describes the HTML that will be used in your page.
Browsers also use the DOCTYPE to determine how to render a page. Not including a DOCTYPE or including an incorrect one can trigger quirks mode.
The kicker here is, that quirks mode in Internet Explorer is quite different from quirks mode in Firefox (and other browsers); meaning that you'll have a much harder job, trying to ensure your page renders consistently with all browsers if the quirks mode is triggered, than you will if it is rendered in standards mode.
Wikipedia has a more in-depth summary of the differences in rendering when using various DOCTYPEs. XHTML is enabled by certain DOCTYPEs, and there is quite a bit of debate about the use of XHTML which is covered well in XHTML — myths and reality.
There are subtle differences between different "standards compliant" rendering DOCTYPEs, such as the HTML5 DOCTYPE (<!DOCTYPE html>, prior to HTML5, only known as the "skinny doctype" which does not trigger standardized rendering in older browsers) and other DOCTYPEs such as this one for HTML 4.01 transitional:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
The DOCTYPE tells the consuming user agent (web browsers, web crawlers, validation tools) what type of document the file is. Using it ensures that the consumer correctly parses the HTML as you intended it.
There are several different DOCTYPES for HTML, XHTML, and Framesets and each of these has two modes Strict and Transitional. Strict says that your markup is using the defined standards exactly. See W3C DTDs page for further details.
Quirksmode is basically the layout method from the browser wars days when the standards were much less respected and defined. Generally a standards mode page, that is valid, will layout more consistently across various browsers, but may lack certain features that you require. One such features is the anchor tag's target attribute. The Quirksmode site is a great resource for these differences.
One final thought is that the new HTML5 standard proposes using a very simple DOCTYPE:
<!DOCTYPE html>
Using this DOCTYPE is a forward compatible way to specify that your pages are in standards mode, and are HTML. This is the method that Google uses, and is reasonably easy to remember. I recommend using this DOCTYPE unless you plan to use XHTML.
A doctype defines which version of HTML/XHTML your document uses. You would want to use a doctype so that when you run your code through validators, the validators know which version of HTML/XHTML to check against. This page provides a good overview:
Don't forget to add a doctype
Common doctypes you can use are listed here:
Recommended list of DTDs
Which doctype you should go with depends on the code you're using, but to get an idea, try running your code through the W3C validator and use the Document Type drop-down menu in the "More Options" menu to try different doctypes out.
W3C Markup Validation Service
In HTML (including XHTML) as used on web pages, DOCTYPE is a string that triggers one of a few browser modes (quirks mode, standards mode, almost standards mode), depending on the exact spelling of the DOCTYPE. You want to use it to select a browser mode that best suits your page.
Formally, in SGML and XML, a DOCTYPE declaration is a reference to a Document Type Definition (DTD), which specifies the formal syntax rules of the markup language. No browser has ever used DTDs for anything or even accessed them. However, they are used by SGML and XML markup validators such as the W3C Markup Validator, except in HTML5 mode. Therefore, the choice of DOCTYPE determines how a validator works if the document is submitted to it. However, the validator mode of operation can also be selected in its user interface. (SGML and XML processors may use DOCTYPEs in different other ways, too, but the question is apparently meant to be limited to the HTML context and to web browsers and closely related software.)
There is no authoritative list of DOCTYPEs. Each HTML specification or draft defines its own DOCTYPE, or DOCTYPEs. The set of DOCTYPEs recognized by browsers when selecting mode varies by browser. In practice, there is no reason to use a DOCTYPE other than <DOCTYPE html> as defined in HTML5, though HTML5 also lists a few “legacy DOCTYPEs”. You can use that DOCTYPE if you want standards mode (recommended for new pages) and use no DOCTYPE if you want quirks mode (which you may need for legacy pages).
“Standards mode” generally means the mode of operation where a browser follows HTML, CSS, DOM and other specifications the best it can. It does not usually mean full conformance. “Quirks mode” is different in different browsers, but generally it means an attempt at imitating the behavior of very old browsers like IE 5. The purpose is to keep old pages working, under the assumption that they may rely on features and bugs in the old browsers. See the description What happens in Quirks Mode? Note that there is a rather different, more limited concept of “quirks mode” in HTML5, which closely resembles the document called Quirks Mode Living Standard.
A typical issue is that element widths are calculated differently in quirks mode and in standards mode. This means that the layout of a page may be more or less changed or even totally messed up, if a page designed to work in quirks mode is viewed in standards mode (or vice versa).
So you should use <!DOCTYPE html> for new pages and keep whatever DOCTYPE (if any) you have been using for old pages.
However, quirks mode means, in some browsers, that many new features of CSS are not supported. This means that if you want to enhance an old page with some CSS3 feature, it may well be necessary to switch to a DOCTYPE that triggers standards mode. In such a case, you need to review and test the page to see whether it will run in standards mode.
A doctype is a document that describes how the contents of a xhtml-like document can look like (like a webpage). Note: this defines only the syntax of said page, the rendering of the page is NOT defined by the DTD!
For example, a doctype could define how the <table>-tag can look like - which attributes it accepts, and which values/valuetypes are accepted for each attribute. Think of it as a lexicon for your current webpage.
Wikipedia has an informative page on the various Doctypes that are in common use. Mind you - there's nothing stopping you from creating your own doctype. The chances are, however, that the browser probably doesn't know how to render your document.
Which DTD to use depends on what you are going to write. XHTML has a whole different DTD than HTML, for example.
Doctypes tell the browser in what language the page is written in, be it HTML or XHTML. For example,
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
tell the browser to render the page as HTML4 strict. Older browsers used to render pages incorrectly and therefore newer browsers simulate errors of the older browsers when they find an old doctype.
Today you should use at least HTML4 or better XHTML.
A blog entry about doctypes is Fix Your Site With the Right DOCTYPE! (from A List Apart).
First of all there is no one doctype you should be using, but most designers try to make it work within XHTML 1.0 Strict.
A doctype is nothing more than a declaration of what tags you can use within your html (though the browsers can use more or less than what is defined) You can actually open up the doctype file and start reading (XHTML 1.0 Strict)
If you do not specify a doctype, the browser will try its best to guess but not always hits the correct type.
Quirks mode is just a technique used by browsers to be backwards compatible, a great example of quirks mode is how IE renders boxes
On the web, a doctype does nothing but tell the brower if you want standards, almost standards, or quirks mode.
What changes in quirks mode depends on the browser: Firefox, Opera, Safari, and Chrome implement a limited set of quirks, like removing the space for text descenders in code like <table><tr><td><img></td></tr></table> (solution: td img { vertical-align:bottom; }). IE, on the other hand, reverts to the rendering engine in IE5.5. That means that you won't be able to use any of the new features implemented since 2000.
To trigger standards mode, I suggest using the HTML5 doctype, <doctype html>, as it is the easiest to remember.
Related
What is DOCTYPE and why do I want to use it?
What are the different DOCTYPEs I can use?
What is the difference between standards and quirks mode, and what are some quirks I may run into with differently set DOCTYPEs?
Lastly, what is the proper DOCTYPE that I should be using?
Basically, the DOCTYPE describes the HTML that will be used in your page.
Browsers also use the DOCTYPE to determine how to render a page. Not including a DOCTYPE or including an incorrect one can trigger quirks mode.
The kicker here is, that quirks mode in Internet Explorer is quite different from quirks mode in Firefox (and other browsers); meaning that you'll have a much harder job, trying to ensure your page renders consistently with all browsers if the quirks mode is triggered, than you will if it is rendered in standards mode.
Wikipedia has a more in-depth summary of the differences in rendering when using various DOCTYPEs. XHTML is enabled by certain DOCTYPEs, and there is quite a bit of debate about the use of XHTML which is covered well in XHTML — myths and reality.
There are subtle differences between different "standards compliant" rendering DOCTYPEs, such as the HTML5 DOCTYPE (<!DOCTYPE html>, prior to HTML5, only known as the "skinny doctype" which does not trigger standardized rendering in older browsers) and other DOCTYPEs such as this one for HTML 4.01 transitional:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
The DOCTYPE tells the consuming user agent (web browsers, web crawlers, validation tools) what type of document the file is. Using it ensures that the consumer correctly parses the HTML as you intended it.
There are several different DOCTYPES for HTML, XHTML, and Framesets and each of these has two modes Strict and Transitional. Strict says that your markup is using the defined standards exactly. See W3C DTDs page for further details.
Quirksmode is basically the layout method from the browser wars days when the standards were much less respected and defined. Generally a standards mode page, that is valid, will layout more consistently across various browsers, but may lack certain features that you require. One such features is the anchor tag's target attribute. The Quirksmode site is a great resource for these differences.
One final thought is that the new HTML5 standard proposes using a very simple DOCTYPE:
<!DOCTYPE html>
Using this DOCTYPE is a forward compatible way to specify that your pages are in standards mode, and are HTML. This is the method that Google uses, and is reasonably easy to remember. I recommend using this DOCTYPE unless you plan to use XHTML.
A doctype defines which version of HTML/XHTML your document uses. You would want to use a doctype so that when you run your code through validators, the validators know which version of HTML/XHTML to check against. This page provides a good overview:
Don't forget to add a doctype
Common doctypes you can use are listed here:
Recommended list of DTDs
Which doctype you should go with depends on the code you're using, but to get an idea, try running your code through the W3C validator and use the Document Type drop-down menu in the "More Options" menu to try different doctypes out.
W3C Markup Validation Service
In HTML (including XHTML) as used on web pages, DOCTYPE is a string that triggers one of a few browser modes (quirks mode, standards mode, almost standards mode), depending on the exact spelling of the DOCTYPE. You want to use it to select a browser mode that best suits your page.
Formally, in SGML and XML, a DOCTYPE declaration is a reference to a Document Type Definition (DTD), which specifies the formal syntax rules of the markup language. No browser has ever used DTDs for anything or even accessed them. However, they are used by SGML and XML markup validators such as the W3C Markup Validator, except in HTML5 mode. Therefore, the choice of DOCTYPE determines how a validator works if the document is submitted to it. However, the validator mode of operation can also be selected in its user interface. (SGML and XML processors may use DOCTYPEs in different other ways, too, but the question is apparently meant to be limited to the HTML context and to web browsers and closely related software.)
There is no authoritative list of DOCTYPEs. Each HTML specification or draft defines its own DOCTYPE, or DOCTYPEs. The set of DOCTYPEs recognized by browsers when selecting mode varies by browser. In practice, there is no reason to use a DOCTYPE other than <DOCTYPE html> as defined in HTML5, though HTML5 also lists a few “legacy DOCTYPEs”. You can use that DOCTYPE if you want standards mode (recommended for new pages) and use no DOCTYPE if you want quirks mode (which you may need for legacy pages).
“Standards mode” generally means the mode of operation where a browser follows HTML, CSS, DOM and other specifications the best it can. It does not usually mean full conformance. “Quirks mode” is different in different browsers, but generally it means an attempt at imitating the behavior of very old browsers like IE 5. The purpose is to keep old pages working, under the assumption that they may rely on features and bugs in the old browsers. See the description What happens in Quirks Mode? Note that there is a rather different, more limited concept of “quirks mode” in HTML5, which closely resembles the document called Quirks Mode Living Standard.
A typical issue is that element widths are calculated differently in quirks mode and in standards mode. This means that the layout of a page may be more or less changed or even totally messed up, if a page designed to work in quirks mode is viewed in standards mode (or vice versa).
So you should use <!DOCTYPE html> for new pages and keep whatever DOCTYPE (if any) you have been using for old pages.
However, quirks mode means, in some browsers, that many new features of CSS are not supported. This means that if you want to enhance an old page with some CSS3 feature, it may well be necessary to switch to a DOCTYPE that triggers standards mode. In such a case, you need to review and test the page to see whether it will run in standards mode.
A doctype is a document that describes how the contents of a xhtml-like document can look like (like a webpage). Note: this defines only the syntax of said page, the rendering of the page is NOT defined by the DTD!
For example, a doctype could define how the <table>-tag can look like - which attributes it accepts, and which values/valuetypes are accepted for each attribute. Think of it as a lexicon for your current webpage.
Wikipedia has an informative page on the various Doctypes that are in common use. Mind you - there's nothing stopping you from creating your own doctype. The chances are, however, that the browser probably doesn't know how to render your document.
Which DTD to use depends on what you are going to write. XHTML has a whole different DTD than HTML, for example.
Doctypes tell the browser in what language the page is written in, be it HTML or XHTML. For example,
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
tell the browser to render the page as HTML4 strict. Older browsers used to render pages incorrectly and therefore newer browsers simulate errors of the older browsers when they find an old doctype.
Today you should use at least HTML4 or better XHTML.
A blog entry about doctypes is Fix Your Site With the Right DOCTYPE! (from A List Apart).
First of all there is no one doctype you should be using, but most designers try to make it work within XHTML 1.0 Strict.
A doctype is nothing more than a declaration of what tags you can use within your html (though the browsers can use more or less than what is defined) You can actually open up the doctype file and start reading (XHTML 1.0 Strict)
If you do not specify a doctype, the browser will try its best to guess but not always hits the correct type.
Quirks mode is just a technique used by browsers to be backwards compatible, a great example of quirks mode is how IE renders boxes
On the web, a doctype does nothing but tell the brower if you want standards, almost standards, or quirks mode.
What changes in quirks mode depends on the browser: Firefox, Opera, Safari, and Chrome implement a limited set of quirks, like removing the space for text descenders in code like <table><tr><td><img></td></tr></table> (solution: td img { vertical-align:bottom; }). IE, on the other hand, reverts to the rendering engine in IE5.5. That means that you won't be able to use any of the new features implemented since 2000.
To trigger standards mode, I suggest using the HTML5 doctype, <doctype html>, as it is the easiest to remember.
In my page, the doctype is declared as:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
no DTD is explicitly specified.
I wonder in IE which DTD will be defaulted?
seems it does not behave the same as
"http://www.w3.org/TR/html4/loose.dtd"
since my table in the page was broken after I added the loose.dtd.
Can anyone help explain this?
Thanks!
By the SGML standard, your document type declaration specifies a Document Type Definition by naming it, as registered by the W3C. However, by the HTML 4.01 spec, a document must have one of three alternative document type declarations, and all of them contain a URL, too.
This is as such just theory, since browsers don’t actually read DTDs. They treat document type declarations just as magic strings, in doctype sniffing. However, in most browsers, the choice of a browser’s mode is affected by the presence or absence of a URL in that magic string for HTML 4.01 Transitional. When it is absent, they operate in Quirks Mode. When it is present, most browsers operate in “standards mode” or “almost standards mode”.
Quirks Mode means a large number of different quirks, so the effect of switching from it to “standards mode” may imply just about anything (varying from no effect to complete disaster). Such a switch generally requires a careful check, if not rewrite, of the entire document.
Your mileage will vary depending on browser and version, but here's the short of it:
To the best of my knowledge, browsers don't actually go to any effort to fetch and make use of the dtd in the URL, or validate the code in any way. Resultingly, your webpage will work "fine" without a doctype declaration, with a broken doctype declaration, and in a number of other broken forms.
When not running your code through a validator, the major reason for providing a doctype definition at the top of your code is to pull browsers out of quirks mode and into standards compliance mode, ala the historical disaster with IE < 7 ...
It's a little bit outside of the scope to lecture on quirks and standards mode here, so the curious should head over to wikipedia:
http://en.wikipedia.org/wiki/Quirks_mode
Web browsers use their own relatively arbitrary standards to switch modes based on the doctype. What you are likely encountering is IE in quirks mode when your DTD lacks a URL, and standards mode when you add the URL.
You should probably aim to include the full declaration, including the URL, and run your code through the W3C validator [1] for good measure.
Fix the rendering problems with valid code and a full doctype [2]. Quirks mode was only ever intended for backwards compatibility so that unmaintained websites will continue to render as expected for as long as possible.
If your web page only renders as expected in quirks mode, your web page is broken.
Sidenote: you should seriously question why you are using 4.01 transitional in 2013.
[1] http://validator.w3.org/
[2] http://www.w3.org/QA/2002/04/valid-dtd-list.html
Does the doctype help to make a webpage more secure? I have used the following:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
So is my page more secure now? How is that? Also the page still shows some warning and errors when I check my page if using the validator server here. So does that mean my page is not secure?
The DOCTYPE has nothing to do with security. The DOCTYPE tells the browser what version of HTML your website is written in so that the browser can display the website accordingly.
The W3C validator is a tool to help find errors that may impact how your website is rendered in various browsers, so fixing any issues you see reported there will only improve usability and how it looks.
No it doesn't. Strict XHTML (or any doctype) does not make your page better, nicer or faster.
Does the doctype help to make a webpage more secure?
No it doesn't. DOCTYPE is not a security feature.
What it does is tell the browser what kind of document it is reading.
If you don't specify any doctype, then IE will drop into quirks mode, meaning that the page will be rendered completely differently do any other browser. You don't want this, so you should specify a doctype. (but for this context, it doesn't matter which doctype)
The XHTML Strict doctype tells the browser that you want your page to be XHTML, and for that to be enforced strictly.
This will (in theory) cause the browser to throw an error if your code does not conform to the XHTML rules, rather than trying to render it anyway. In theory this makes your code better because you can pick up errors more easily. However many browsers don't actually enforce it, meaning that the whole "strict" thing is fairly irrelevant. XHTML is no longer considered best practice, and most people have moved on from this now, and are using the HTML5 doctype instead.
No, adding a doctype declaration does not affect security the least. If your page “still shows some warning and errors when [you] check [your] page”, it simply means that the page does not conform to the document type definition that you refer to by the doctype declaration.
Validation is a purely formal thing, and the impact of violation validity requirements depends on the kind of violation. (The impact varies from no impact to total collapse.)
The use of a doctype declaration is, as far as browsers are considered, just a magic incantation that triggers “standards mode”, “almost standards mode”, or “quirks mode”, depending on browser and doctype. It’s a fairly complex issue, but the XHTML 1.0 doctype you mention triggers “standards mode”, and the absence of any doctype triggers “quirks mode”, which is really just a common name for many kinds of quirks and oddities that browsers do in trying to emulate bugs in browser versions from the 20th century.
No DOCtype is not related to security concern. To get clear conception of it, you might like this article http://www.alistapart.com/articles/doctype/
What does <!DOCTYPE> describe other than the version of HTML being used and if excluded what are the consequences?
The doctype basically tells the browser that the page is compliant with HTML standards. Omitting the doctype can make certain browsers (chief among them, Internet Explorer) go haywire and fall back to a "Quirks Mode", in which HTML elements aren't rendered to standard.
In the Quirks mode the browsers violate contemporary Web format specifications in order to avoid “breaking” pages authored according to practices that were prevalent in the late 1990s. Different browsers implement different quirks. In Internet Explorer 6, 7, 8 and 9, the Quirks mode is effectively frozen IE 5.5. In other browsers, the Quirks mode is a handful of deviations from the Almost Standards mode.
Further reading: http://hsivonen.iki.fi/doctype/
if there is no presented. IE will use "Quirks mode" by default. (You can you F12 in IE to see the current mode.)
And in quirks mode many css rule is different.
Here's an article about Quirks mode and strict mode
There is not just one type of HTML, there are actually many: HTML 4.01 Strict, HTML 4.01 Transitional, XHTML 1.0 Strict, and many more. All these types of HTML are defined in their respective W3C specifications
Why specify a doctype? Because it defines which version of (X)HTML your document is actually using, and this is a critical piece of information needed by some tools processing the document.
For example, specifying the doctype of your document allows you to use tools such as the Markup Validator to check the syntax of your (X)HTML. Such tools won't be able to work if they do not know what kind of document you are using.
For knowing about the usage and importanse of DOCTYPE see the link link
Always add the declaration to your HTML documents, so that the browser knows what type of document to expect.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
HTML: What is the functionality of !DOCTYPE
I recently asked a question here and the solution was a simple:
You need to add a doctype to the page. This should fix the issue for you.
Now, my pages work fine in every browser without the doctype (except IE). Does IE need a doctype (is this an IE only thing) and do other browsers just assume it OR or is it doing something I'm not seeing.
What are its functions and how does it work?
All browsers need the doctype. Without the DOCTYPE you are forcing the browsers to render in Quirks Mode.
However, DOCTYPE was only partially used by the browsers in determining dialect and parsing, even though that was the purpose. This is why HTML5 has reduced the DOCTYPE to simply:
<!DOCTYPE html>
2.2. The DOCTYPE
The HTML syntax of HTML5 requires a DOCTYPE to be specified to ensure that the browser renders the page in standards mode. The DOCTYPE has no other purpose and is therefore optional for XML. Documents with an XML media type are always handled in standards mode. [DOCTYPE]
The DOCTYPE declaration is <!DOCTYPE html> and is case-insensitive in the HTML syntax. DOCTYPEs from earlier versions of HTML were longer because the HTML language was SGML-based and therefore required a reference to a DTD. With HTML5 this is no longer the case and the DOCTYPE is only needed to enable standards mode for documents written using the HTML syntax. Browsers already do this for <!DOCTYPE html>.
Source: HTML5 differences from HTML4: DOCTYPE
The Doctype does two things.
It identifies which dialect of HTML you're using.
It controls whether the browsers uses "standards" or "quirks" mode to render the document.
If there is no doctype, or there's an unrecognized one, then it uses "quirks" mode and interprets the document as best it can. If there IS a doctype, and it recognizes it, then it follows the standards. The results of the rendering can vary depending on how it interprets the document.
Why?
Why specify a doctype? Because it
defines which version of (X)HTML your
document is actually using, and this
is a critical piece of information
needed by some tools processing the
document.
For example, specifying the doctype of
your document allows you to use tools
such as the Markup Validator to check
the syntax of your (X)HTML. Such tools
won't be able to work if they do not
know what kind of document you are
using.
But the most important thing is that
with most families of browsers, a
doctype declaration will make a lot of
guessing unnecessary, and will thus
trigger a "standard" rendering mode.
Source: http://www.w3.org/QA/Tips/Doctype
You should have a DOCTYPE for ANY browser. It tells the browser how to interpret the html and css. This is why html4 and html5 have different definitions (as does xhtml). All very important for validation.
What IE will do is put the document into what it calls 'quirks mode' which basically ignores a whole heap of rules for how CSS should (by modern definitions) behave. Here is a good summary of the issue. It harks back to the bad old days of non-standardised CSS support
Browsers need at the least to render in what is known as standards mode. See John Resig's article on the html 5 doctype: http://ejohn.org/blog/html5-doctype/. Now if you want your browser to not use standards and render like its 1990 go ahead and not add anything and you will see floats and other now standard items not work correctly. If you want to have your page render/validate in accordance to a particular standard then you would want to add more to the doc type but it is not necessary.
From W3Schools, a doctype is "an instruction to the web browser about what version of the markup language the page is written in." (http://www.w3schools.com/tags/tag_doctype.asp)
If you do not include the doctype, the browser may assume you are using a different language than you really are, causing it to be rendered incorrectly.
From W3Schools.com:
The doctype declaration is not an HTML
tag; it is an instruction to the web
browser about what version of the
markup language the page is written
in.
There are a handful of different doctypes, and changing them can drastically change how your page renders.
The doctype declaration should be the
very first thing in an HTML document,
before the tag.
The doctype declaration is not an HTML
tag; it is an instruction to the web
browser about what version of the
markup language the page is written
in.
The doctype 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.
Reference