Тег <!DOCTYPE>
Этот тег определяет тип документа.
HTML 4.01
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"><html><head>-
<metacharset="utf-8"/> -
<title>New Page</title> </head><body></body></html>
HTML 5
<!DOCTYPE html><html><head>-
<metacharset="utf-8"/> -
<title>New Page</title> </head><body></body></html>