Adding the Doctype.
The <!DOCTYPE>
declaration should always be included at the top of the HTML document, before the <html>
tag.
See HTML 5 Doctype for details on the HTML 5 Doctype.
<!DOCTYPE html>
See HTML 4.01 Doctypes for details on how these types differ from each other.
Strict
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
Transitional
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
Frameset
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN" "http://www.w3.org/TR/html4/frameset.dtd">