The Importance of HTML / XHTML Validation
Copyright Herman Drost 

Part One I discussed the Benefits of HTML Validation.

For Part Two I will discuss:

A. What to validate your web pages for
B. The validation process
C. Validation Tools
D. Common validation errors

A. What to validate your web pages for:

1. Doctype
2. HTML or XHTML document ( or other coding languages you
have used)
3. CSS style sheet
4. Links
5. Browsers
6. Screen Resolution
7. Connectivity

Here's an example of a web site I recently designed
which has correctly validated XHTML and CSS:

http://www.discount-real-estate-listings-md.com/

2. Validate your HTML or XHTML document ( and other coding
languages you have used).

If you validate your code it will make it easier for:

- search engines to index your web pages
- pages to load faster
- make your pages accessible for other devices that surf
the Web.
- checking coding errors by running your pages through a
validator.

3. Validate your Cascading Style Sheets (CSS).

If there are errors in your CSS, the layout of your web
pages will be affected and your site will not appear correctly
when viewed in any of the main browsers.

4. Validate your links

Broken links in your web pages will:

- frustrate your visitors when searching for relevant
information from your site.
- affect search engine rankings. When spiders can't index
the links on your site they won't find your keyword rich
web pages.

5. Check browser compatibility

The main browsers you should design your web site for
include: Internet Explorer (IE6, IE5), Firefox, Opera, and
Netscape (Mozilla).

This is according to the current statistics taken from:
http://www.w3schools.com/browsers/browsers_stats.asp

6. Test for different screen resolutions

The current trend is that more and more computers are using
a screen size of 1024x768 pixels:

Here are the stats for June 2005:

1024x768..............................56%
800x600...............................28%
Higher than 1024x768............11%

7. Check connectivity speeds

Web pages that contain a large number of graphics or
tables, use flash or video, will load slowly or sometimes
not at all with a dial up connection but will be fine with a
cable or dsl connection. Although the trend is towards
people converting to high speed connections many still
use dial-up to surf the Net for information. Therefore
design your site for both.

C.Validation Tools

HTML/XHTML validation
http://www.validator.w3.org/

CSS validation
http://jigsaw.w3.org/css-validator/

Link checker
http://validator.w3.org/checklink

Browser Compatibility
http://www.anybrowser.com

Connectivity Test
http://www.websiteoptimization.com/services/analyze/
http://www.netmechanic.com/maintain.htm

D.Common HTML/XHTML validation errors

Improper Nesting of Tags

This is a very common error. You should close tags your in
the reverse of the order you opened them:
<xx><yy>content</yy></xx>.

An easy error to make, but it's easy to fix, too.

Missing alt tags

You should include alt tags for all your images with a text
description so that visitors will still know what the image is
about even if they turn off viewing images in their browser.

Improper closing of tags

ie <p>This is a paragraph<p>. The end tag should be </p>
It will validate in html, but not xhtml.

For XHTML 1.0 validation it's easy to omit these closing
tags:

<br /> or <hr /> or <img src="xx.gif" />

Margin height and width

marginheight="0"
^Error: there is no attribute "MARGINHEIGHT" for this
element. Use CSS to fix this error.

marginwidth="0"
^Error: there is no attribute "MARGINWIDTH" for this
element. The only fix for this is to utilize CSS and absolute
positioning.

Horizontal Line Color

<hr size="1" color="#C0C0C0">
^Error: there is no attribute "COLOR" for this element.

This can only be fixed with CSS.

ie <div
style="color:#000;background-color:#C0C0C0;height:1px;font-size:1px;">
</div>

Border Color

bordercolor="#ffffff"
^Error: there is no attribute "BORDERCOLOR" for this
element. This can only be fixed with CSS.

Unescaped Ampersand (XHTML)
Always use &amp; in place of &.

Conclusion:

If you get into the habit of always validating your web
pages, your web site will be faster loading, more
search engine friendly, accessible to a greater number of
devices and therefore appeal to a larger number of visitors.
=====================================================
Herman Drost is a Certified Internet Webmaster (CIW)
and owner of iSiteBuild.com
Web Site Design, Web Hosting, Web Site Promotion