HTML and CSS Reference
The W3 Validator.
If you look closely at the screenshot, you can see that at the time I validated this page, it
came out with 42 errors, all of which are violations of the XHTML 1.0 Transitional rec-
ommendation. The page looks fine in the popular browsers, but it's not in sync with the
recommendation. The errors generally fall into two categories: missing closing tags (usu-
ally for the <img> tag) and missing required attributes (mainly the alt attribute for <img>
tags). This page also includes some invalid attributes for tags. One common error that
appears on this page refers to an entity with no system identifier, and a longer set of
errors related to the same bit of markup. The problem here is that the validator expects
the character & to be the beginning of an entity, but on this page, it is part of the URL for
a link. To avoid these errors, the ampersands in links need to be encoded as & .
You can see this entity-related error in Figure 18.2.