XHTML language is derived from Extensible Markup Language (XML) which creates markup languages, and can have an optional XML declaration at start.
<?xml version=”1.0” encoding=”UTF-8” ?>
If included then this declaration should be at the start of document and nothing above it. Encoding attribute tells about the encoding used in web document to represent characters for display. Encoding is mentioned as different hardware and software uses different method to represent character (or encoding).