... closed, every attributemust have a value, and more. XHTML 1. 1 requires that HTML documents also be validXML.Technically, XHTML 1. 1 and HTML 4. 01 are very similar. The tags and attributes arealmost ... this book, as I introduce each tag, I explain any browser-specific issues you may encounter.The Current Standard: XHTML 1. 1XHTML 1. 1 is written in Extensible Markup Language (XML), and is ... aheading.What HTML Is (And What It Isn’t) 51 3Although HTML doesn’t say much about how a page looks whenit’s viewed, Cascading Style Sheets (CSS) enable you to applyadvanced formatting to HTML tags. HTML...