Uppercase or lowercase doctype?
doctype, html
Solution
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 html>
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.
Problem
When writing the HTML5 doctype what is the correct method? ``` <!DOCTYPE html> ``` or ``` <!doctype html> ```