HTML and CSS Reference
There are several advanced settings of the Markup Validation Service you can use for your standardization
projects. The (X)HTML source code can be displayed with the error messages directly linking to the corresponding
lines. This is a useful feature for developers. The tree structure of document headings can be visualized by the outline
option, which makes it easier to realize which header is missed (if any). Custom 404 error pages sent by the server
can be validated by ticking the checkbox “Validate error pages.” Beyond the concise reports provided by default, more
explanations and longer suggestions can be requested with the Verbose Output option. Another option of the
W3C Markup Validation Service is to correct markup errors using the HTML Tidy tool discussed in Chapter 11.
Beyond the error location, the Markup Validation Service gives hints for corrections and links to the
corresponding specifications and FAQs (Figure 14-2 ). Some of the characters might be highlighted, which is another
aid, and sometimes makes the detection of invalid characters very easy.
Figure 14-2. The W3C Markup Validation Service clearly indicates error locations and provides useful hints
The markup validation results and suggestions are useful not only for the less experienced developers but also
for experts. Using the line numbers, it is fairly easy to find errors, which is a prerequisite for correcting them even for
those who do not rely on the correction tips.
After the necessary corrections and the final revalidation, the result should look like Figure 14-3 .