Why do I need to write W3C standard code?
If you care to reach the largest audience for the longest time possible, you want to work with web standards, and where document structure and layout are concerned, XHTML & CSS are the way to go.
the W3C have set certain web standards all based on good development practices. if your website is not fully W3C compliant in accordance to a certain document type then according to the standards devised you have some bad practices in your development.
As an example : not closing an HTML tag is considered a bad development practice.
a widely recognized document type standard is the XHTML 1.0 Strict
I usually code all my HTML in accordance with the W3C standards in XHTML 1.0 Strict Document Type.
Another example is that all image tags should have an “alt” property like so
<img src=”company-logo.jpg” alt=”Our Company Logo” />
Notice that I closed this HTML tag with a “/>”
an HTML tag with no child elements ( text nodes are considered child elements ) should be closed in that manner.
another example :
<p>
this is a text node
</p>
There is also the global accessibility guidelines called W3C WCAG 2.0. These guidelines are specific to websites and web applications. The W3C website contains a lot of resources and information for developers on how to implement accessibility.