ASP.NET allows you to create Web pages that are compliant with XHTML 1.1 standards. For more information about the XHTML 1.1 standard, see the W3C site. By default, when you are working with browsers that support HTML 4.0 or later, ASP.NET pages and controls render markup that is compatible with the XHTML 1.0 Transitional standard. However, under some circumstances, you might not want ASP.NET to render XHTML markup. This is typically true when you have existing pages that rely on tags or attributes that would ordinarily be prohibited by XHTML.