Attributes of the <!DOCTYPE html> Declaration
The <!DOCTYPE html>
tag is an SGML declaration and therefore does not have any named attributes like those used when coding other HTML tags.
The tag name of the top element of the HTML document follows the DOCTYPE
keyword.
<!DOCTYPE html>
The PUBLIC
identifier should never be coded on the DOCTYPE declaration.
If software generating HTML code requires that either a PUBLIC
or SYSTEM
identifier be included, then the SYSTEM
keyword may be coded followed by the value "about:legacy-compat"
enclosed in double quotes.
<!DOCTYPE html SYSTEM "about:legacy-compat">