HTML and CSS Reference
Figure 1-4. Validating an HTML5 document
Note that this tool may not correctly validate ASP.NET server-side markup. For example, the
runat=”server” attribute may be flagged as an error. If you're using Visual Studio, your job is simpler
because validation errors are automatically highlighted as you key in your markup (see Figure 1-5).
Figure 1-5. HTML5 document validation in Visual Studio
n Note You might wonder why HTML pages created in Visual Studio have xmlns set to http://www.w3.
org/1999/xhtml . This namespace indicates that an HTML5 document is using validation rules from the XHTML5
specifications; Visual Studio editor flags validation errors accordingly.