Validation - Web Standards: Mastering HTML5, CSS3, and XML - page 440

Figure 14-3. The green stripe and the result “Passed” indicate that the markup is valid

■ Validating htMl5 is still an experimental feature at the W3C Markup Validation Service, and the validator will
give a warning (not error) even if the web page being analyzed is valid. the validator does not recognize rdFa annotations
in htMl5, nor XhtMl5 documents. 3 Furthermore, in contrast to valid XhtMl documents, the validator does not provide
validation badges with hyperlinks for valid htMl5 documents. as will be discussed later, such badges can be downloaded
from a separate site.

Note

The W3C Markup Validator is not only free but also open source and available under the W3C Software
License [4]. Anyone is welcome to set up mirrors of the service or contribute to its development.
Although there are other markup validators on the Web, such as the WDG HTML Validator [5], or offline tools such
as Firefox's HTML Validator plug-in [6], using the W3C Markup Validation Service is recommended. It is part of W3C
Unicorn, which can be used if styles sheets and feed channels are also validated (see later in section “W3C Unicorn”).

3 The XML declaration and all namespace declarations provided in XHTML5 result in an error message, even if they are valid.
Moreover, the validation result of XHTML5 documents states HTML5 instead of XHTML5.