A HTML File consists two parts
HTML Document
1 HTML Version
2 HTML Document
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<HTML>
HTML Content
....
</HTML>
HTML Document is a HTML Element whose content consists of Head Element and Body Element, and is contained between HTML Document Opening Tag <HTML> and HTML Document Closing Tag</HTML>.
A HTML Tag is divided into HTML Opening Tag (HOT) and HTML Closing Tag (HCT)
A HTML Tag consist of three parts: Tag Opening Identifier (TOI), Tag Content and Tag Closing Identifier (TCI).
The Tag Opening Identifier of HTML Opening Tag is less than symbol (<) and the Tag Closing Identifier of HTML Opening Tag is bigger than symbol (>).
The Tag Opening Identifier of HTML Closing Tag is less than symbol followed by slash (<\) immediately and the Tag Closing Identifier of HTML Closing Tag is bigger than symbol (>) too.
Tag Content contains Tag Name and attributes. Tag Name is a string, which is case-insensitive. Attributes is the property of presenting the Content enclosed by HOT and HCT
Ex: HTML Document Opening Tag <HTML>, HTML Document Closing Tag</HTML>
HTML Document Content consist of two HTML Elements: Head Element and Body Element.
http://www.w3.org/TR/html401/struct/global.html