When writing the HTML5 doctype what is the correct method?
<!DOCTYPE html>
or
<!doctype html>
In HTML, the DOCTYPE is case insensitive. The following DOCTYPEs are all valid:
<!doctype html> <!DOCTYPE html> <!DOCTYPE HTML> <!DoCtYpE hTmL>
In XML serializations (i.e. XHTML) the DOCTYPE is not required, but if you use it, DOCTYPE should be uppercase:
DOCTYPE
See The XML serialization of HTML5, aka ‘XHTML5’:
Note that if you don’t uppercase DOCTYPE in an XHTML document, the XML parser will return a syntax error. The second part can be written in lowercase (html), uppercase (HTML) or even mixed case (hTmL) — it will still work. However, to conform to the Polyglot Markup Guidelines for HTML-Compatible XHTML Documents, it should be written in lowercase.
Note that if you don’t uppercase DOCTYPE in an XHTML document, the XML parser will return a syntax error.
The second part can be written in lowercase (html), uppercase (HTML) or even mixed case (hTmL) — it will still work. However, to conform to the Polyglot Markup Guidelines for HTML-Compatible XHTML Documents, it should be written in lowercase.
html
HTML
hTmL
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