An example DOCTYPE below.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
A Document Type Declaration, or DOCTYPE, is an instruction that associates a particular HTML file with a Document Type Definition (DTD) (for example, the formal definition of a particular version of HTML).
In the serialized form of the document, it manifests as a short string of markup that conforms to a particular syntax.
A DOCTYPE is always the first line in the file.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<HTML>
<HEAD>
<TITLE>My Webpage</TITLE>
</HEAD>
....
The are many DOCTYPEs in the Snippets library ready for use. This is especially useful in FreeCode where the DOCTYPE may need to be altered manually.