I found in most of html 4.0 page ,the doc header writes like that\[code\]<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">\[/code\]but in some pages which includes the html5 tags .The header is shorter\[code\]<!DOCTYPE html>\[/code\]What's the difference between two of them?