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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
Related
when using Perl CGI, it always print out the: <"DOCTYPE html ".... > header before printing out the rest of the html body, which messes up the proper display of the web page. I guess the cause is the DOCTYPE still references a very old version of HTML. This first line get generated regardless when I use $query->start_html(...);. So the question is, how to prevent that <!DOCTYPE...> line from being generated? When I delete that DOCTYPE line, my web page runs properly after that. Any insight is greatly appreciated. Thanks!
Browsers will use the DOCTYPE definition to decide whether or not to interpret an HTML (or XHTML) document in Quirks mode. I assume that's what you mean by "messes up the proper display of the web page" - you're carefully creating valid HTML5 but the browser goes into Quirks mode and the page doesn't look right.
What you want is the standard HTML DOCTYPE definition.
<!DOCTYPE html>
Unfortunately for you, the HTML generation functions in CGI.pm are unmaintained and don't have support for HTML5. So you can't get the module to generate this DOCTYPE.
Honestly, your best approach is to stop using all of the HTML generation functions and switch to a template-based approach instead. But I can see how that would be a big job so, in the short term, perhaps you can just stop using start_html(). It shouldn't be too hard to replace the call with a heredoc that contains the text that you want.
Update: The comment from Quentin below got me thinking. When I said:
you're carefully creating valid HTML5 but the browser goes into Quirks mode and the page doesn't look right
I was completely wrong. If you get the browser behaviour you want without a DOCTYPE, then you want to put the browser into Quirks mode. And that's far easier. Using the information from the Wikipedia article I linked to above, you can see that HTML 4.01 Transitional is the most recent DOCTYPE that will put all modern browsers into Quirks mode. So you can use that DOCTYPE.
$ perl -MCGI=:html -E'say start_html(-dtd => "-//W3C//DTD HTML 4.01 Transitional//EN")'
<!DOCTYPE html
PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head><title>Untitled Document</title>
</head>
<body>
And that should get the browsers working as you want them.
But relying on Quirks mode is fragile. I recommend that you consider fixing your HTML and CSS so that they work as you want when browsers are in Standards mode.
I have seen bunch of HTML email templates example and all of them use <table> element for layout. Is there any specific reason for using <table>? I tried making one without it and it works for me. Should I be worried that it might break for someone else with different browser?
The main reason tables are still used nowadays is to support Outlook 2007/2010/2013. Those versions use Microsoft Word engine to render HTML, and it's quite a mess. It has a limited support for CSS (no float or position for example), and some CSS properties are only supported on some specific HTML elements. For example, padding is supported on a , but not on a . And even when you could theorically use padding on more semantical elements (like tags), or use margin on elements instead, Word's rendering engine is still massively bugged and can have unpredictable behavior with such HTML and CSS code. Thus, developers find it easier to just use instead.
But here's the thing : if you don't feel like you need to support Outlook 2007/2010/2013, then you can absolutely ditch tables and use better code instead. And even if you need to support it, simple one-column layouts can be done without tables. The reason your template works in Outlook 2011 is that this version (for Mac only) uses WebKit rendering engine (just like in Safari or Apple Mail).
Referring to this old post(why-is-it-still-recommended-to-use-tables-for-email-structure) and some of my own experiments:
We can definitely use HTML tags and not just <table> tag. It gets rendered well in modern browsers. I have personally experimented with Chrome ( which most probably means it works on all chromium based browsers ) and Safari.
Another thing I noticed is, the email clients stripped the template and removed all tags except the main content. In other words, it only rendered what's inside the <body> tag and removed other tags like <html>, <head> including the <body> tag itself. So I don't use those tags in my template at all.
I am looking for something, like a good starting point for this question:
Which DOCTYPE should be used when I use schema.org?
Until now I have changed this:
DOCTYPE html PUBLIC "- // W3C // DTD XHTML 1.0 Transitional // EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"
into this:
DOCTYPE html PUBLIC "- // W3C // DTD XHTML + RDFa 1.0 // EN" "http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd"
But, what would be best practice here?
schema.org doesn't explicitely recommend a doctype. I'd recommend to switch to an HTML5 doctype:
<!DOCTYPE html>
It will be compatible with both microdata and RDFa 1.1 syntaxes which are useful for schema.org integration. (microdata is currently the only one shown in the examples though).
That was before XHTML5. If you prefer xml over html, start with xml declaration and serve content with MIME type application/xhtml+xml Particularly remember using < link rel="profile" href="http://www.w3.org/1999/xhtml/vocab"/> so user-agent web-browser will know to use new initial context, that, to date has never required separate rel="profile" for RDFa. Without new initial context, older doctype technique should work with quirks. For schema.org, prefix schema is predefined by RDFa initial context http://www.w3.org/2011/rdfa-context/rdfa-1.1 while schema.org documentation misleads into using microdata instead of RDFa. Schema helps search engines indexing aspects besides domain-specific ones, such as about page and web page with greater depth than markup tags.
It seems sometime to work fine and sometimes not, so in should I use divs inside form or not?
and in general is there a guide for what HTML tags will not work inside other tags?
Divs do not cause any intrinsic problems inside forms. Any CSS rules or JS that might get applied to them may cause problems, but the same is true of any element.
The HTML 4.01 specification includes a guide on how to read DTDs. This is applicable for HTML 3.2 and 4.x as well as XHTML 1.x. HTML 5 does not have an official DTD, so you have to pay attention to the "Content model" for each element in the spec.
Update: Please disregard, my problem was caused by an advertisement bar being inserted by the vendor who provides my workplace wireless service.
I was building a mobile friendly website and wanted to use HTML 5. However when I specify the doctype as <!DOCTYPE HTML> , I get a gap at the top of the page on safari on the iphone.
I notice that other sites have the same problem such as nextstop.com and nike.com
I guess safari does not fully support HTML 5 yet. Anybody know of a workaround?
HTML 5 is still in a very unstable state. Don't use it in a production environment.
Edit Just so you guys know what it's about, HTML 5 is currently an Editor's Draft, and the document clearly states (in the Status of This Document section) that this specification is not stable, and that a consensus may not have been reached on any of the proposed sections. I think it should be clear enough that it means it's a bit early to start using it.
All browsers correctly interpret the HTML doctype. Putting it in sets your browser into Standards Compliant mode, that is the only difference with or without the doctype.
You can use a CSS reset tool like http://meyerweb.com/eric/tools/css/reset/ to get rid of default margins and padding on all elements.