<html> <head> <!DOCTYPE HTML PUBLIC "version name" "url"> </head> <body></body> <html>
它定义了文件将用何种语言解释,它在这个HTML,XHTML,XML还不能完全统一的情况下至关重要。下面举两个例子: HTML:<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 //EN" "http://www.w3.org/TR/html4/strict.dtd"> XHTML:<!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> XML:<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">