- Posted by lio on October 5, 2008
Validate XHTML With A DTD
An XHTML document is validated against a Document Type Definition (DTD). Before an XHTML file can be properly validated, a correct DTD must be added as the first line of the file.
The Strict DTD includes elements and attributes that have not been deprecated or do not appear in framesets:
!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"
The Transitional DTD includes everything in the strict DTD plus deprecated elements and attributes:
!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"
The Frameset DTD includes everything in the transitional DTD plus frames as well:
!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd"
This is a simple XHTML document:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<title>simple document</title>
</head>
<body>
<p>a simple paragraph</p>
</body>
</html>
|
- Posted by lio on October 5, 2008
How W3Schools Was Converted To XHTML
W3Schools was converted from HTML to XHTML the weekend of 18. and 19. December 1999, by Hege Refsnes and Ståle Refsnes.
To convert a Web site from HTML to XHTML, you should be familiar with the XHTML syntax rules of the previous chapters. The following steps were executed (in the order listed below):
A DOCTYPE Definition Was Added
The following DOCTYPE declaration was added as the first line of every page:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> |
Note that we used the transitional DTD. We could have chosen the strict DTD, but found it a little too "strict", and a little too hard to conform to.
A Note About The DOCTYPE
Your pages must have a DOCTYPE declaration if you want them to validate as correct XHTML.
Be aware however, that newer browsers (like Internet Explorer 6) might treat your document differently depending on the <!DOCTYPE> declaration. If the browser reads a document with a DOCTYPE, it might treat the document as "correct". Malformed XHTML might fall over and display differently than without a DOCTYPE.
Lower Case Tag And Attribute Names
Since XHTML is case sensitive, and since XHTML only accepts lower case HTML tags and attribute names, a general search and replace function was executed to replace all upper case tags with lowercase tags. The same was done for attribute names. We have always tried to use lower case names in our Web, so the replace function did not produce many real substitutions.
All Attributes Were Quoted
Since the W3C XHTML 1.0 Recommendation states that all attribute values must be quoted, every page in the web was checked to see that attributes values were properly quoted. This was a time-consuming job, and we will surely never again forget to put quotes around our attribute values.
Empty Tags: <hr> , <br> and <img>
Empty tags are not allowed in XHTML. The <hr> and <br> tags should be replaced with <hr /> and <br />.
This produced a problem with Netscape that misinterpreted the <br/> tag. We don't know why, but changing it to <br /> worked fine. After that discovery, a general search and replace function was executed to swap the tags.
A few other tags (like the <img> tag) were suffering from the same problem as above. We decided not to close the <img> tags with </img>, but with /> at the end of the tag. This was done manually.
The Web Site Was Validated
After that, all pages were validated against the official W3C DTD with this link: XHTML Validator. A few more errors were found and edited manually. The most common error was missing </li> tags in lists.
Should we have used a converting tool? Well, we could have used TIDY.
Dave Raggett's HTML TIDY is a free utility for cleaning up HTML code. It also works great on the hard-to-read markup generated by specialized HTML editors and conversion tools, and it can help you identify where you need to pay further attention on making your pages more accessible to people with disabilities.
The reason why we didn't use Tidy? We knew about XHTML when we started writing this web site. We knew that we had to use lowercase tag names and that we had to quote our attributes. So when the time came (to do the conversion), we simply had to test our pages against the W3C XHTML validator and correct the few mistakes. AND - we have learned a lot about writing "tidy" HTML code.
- Posted by lio on October 5, 2008
The XHTML standard defines three Document Type Definitions.
The most common is the XHTML Transitional.
<!DOCTYPE> Is Mandatory
An XHTML document consists of three main parts:
- the DOCTYPE
- the Head
- the Body
The basic document structure is:
<!DOCTYPE ...>
<html>
<head>
<title>... </title>
</head>
<body> ... </body>
</html>
|
The DOCTYPE declaration should always be the first line in an XHTML document.
An XHTML Example
This is a simple (minimal) XHTML document:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head> <title>simple document</title> </head>
<body> <p>a simple paragraph</p> </body>
</html>
|
The DOCTYPE declaration defines the document type:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
|
The rest of the document looks like HTML:
<html>
<head> <title>simple document</title> </head>
<body> <p>a simple paragraph</p> </body>
</html>
|
The 3 Document Type Definitions
- DTD specifies the syntax of a web page in SGML.
- DTD is used by SGML applications, such as HTML, to specify rules that apply to the markup of documents of a particular type, including a set of element and entity declarations.
- XHTML is specified in an SGML document type definition or 'DTD'.
- An XHTML DTD describes in precise, computer-readable language, the allowed syntax and grammar of XHTML markup.
There are currently 3 XHTML document types:
- STRICT
- TRANSITIONAL
- FRAMESET
XHTML 1.0 specifies three XML document types that correspond to three DTDs: Strict, Transitional, and Frameset.
XHTML 1.0 Strict
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
|
Use this when you want really clean markup, free of presentational clutter. Use this together with Cascading Style Sheets.
XHTML 1.0 Transitional
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
Use this when you need to take advantage of HTML's presentational features and when you want to support browsers that don't understand Cascading Style Sheets.
XHTML 1.0 Frameset
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
|
Use this when you want to use HTML Frames to partition the browser window into two or more frames.