XHTML has replaced HTML for building web pages, but older pages can be converted manually or with software. Different versions of XHTML support different features, and it’s important to choose the appropriate version and verify the document with an XHTML validator. XHTML 1.0 Transitional allows for some tags and presentation attributes found in earlier HTML standards, while XHTML 1.0 Strict and 1.1 do not support any presentation elements. Pages must have a DTD and an XML namespace declaration to be valid XHTML, and an XHTML validator will detect any errors.
The eXtensible HyperText Markup Language (XHTML) has replaced the similar HyperText Markup Language (HTML) as the markup language of choice for building web pages, but older web pages are relatively easy to convert from HTML to XHTML. First, choose the appropriate version of XHTML to convert to because different versions support different features. Then make code changes manually to better understand the new language’s syntax rules, or use a software tool to convert the pages for you. In both cases, it is a good idea to verify that the document has been converted correctly with an XHTML validator, which can detect any errors in the code.
Keep in mind that just like HTML, XHTML has several versions and not all of them support the same functionality. XHTML 1.0 Transitional allows for some tags, elements, and presentation attributes found in earlier HTML standards, including the tag and “center” attributes. If you are upgrading from HTML to XHTML 1.0 Strict or XHTML 1.1, remove any presentation tags or elements and recreate the look you want using cascading style sheets because these versions of XHTML do not support any presentation elements.
For a simple web document, you can do an HTML to XHTML conversion manually. If you’re new to XHTML, this can also help you familiarize yourself with the language’s stricter syntax rules. To comply with these stricter requirements, make sure all tags are lowercase, properly nested, and closed with a slash. Also, all values must be enclosed in quotes. The “find and replace all” option available in most text editors and web development programs can help you make these changes.
The software can also convert your code from HTML to XHTML with just a few clicks. Most professional web design programs have this option, often in the “File” or “Tools” menu. A popular tool called HTML Tidy, originally released by members of the World Wide Web Consortium (W3C), is free to download and will clean up and convert between popular web formats. You may also be able to find some online tools that can switch documents from one markup language to another.
Whether you choose to edit your documents by hand or use software to do the HTML to XHTML conversion, there are a few things you should check before publishing your pages on the web. To be valid XHTML, a page must have both a Document Type Definition (DOCTYPE or DTD) and an XML namespace declaration. Each of these will depend on the version of XHTML you use, so do a little research to figure out what these elements should look like. An XHTML validator, available in most web development software and on the W3C website, will inform you of any errors or omissions in your code.
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