The correct syntax of the DOCTYPE declaration in HTML5 is:
html
<!DOCTYPE html>
This declaration must appear at the very beginning of every HTML document
before the <html> tag. It is not an HTML tag but an instruction to the
browser about the document type and version of HTML being used, enabling
standards mode rendering
. The DOCTYPE declaration is case-insensitive, so variations like <!doctype html>, <!Doctype html>, or <!DocType html> are all valid
. For older versions of HTML, such as HTML 4.01 or XHTML, the DOCTYPE declaration is more complex and includes references to a Document Type Definition (DTD), for example:
html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
or
html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
However, these older forms are largely obsolete with the adoption of HTML5
. Summary:
- HTML5 DOCTYPE:
<!DOCTYPE html> - Must be the first line in the HTML document
- Case-insensitive
- Older HTML versions use longer, DTD-referencing DOCTYPEs
This simple declaration ensures browsers render the page in standards mode rather than quirks mode
