The 2 content preambles of HTML

The 2 elements that specify the preamble of a webpage are doctype, and html.

#1, Doctype

The Doctype element specifies the document type. When omitted, browsers tend to use a different rendering mode that is incompatible with some specifications.

For HTML documents, the doctype is "html". Since HTML version 5, you do not need to add a legacy string. This declaration comes first on a document.

<!DOCTYPE html> 

#2, HTML

The html element specifies the document root. It comes after the document type and it will contain both the metadata and data window of the document.

<!-- document type comes here -->  
<html>  
    <!-- document metadata comes here -->  
    <!-- document window comes here --> 
</html> 

Summary

Your document preamble should have the structure below.

<!DOCTYPE html> 
<html>  

</html>