There are other Document Type Definitions to work with such as HTML 4.0 Transitional for greater flexibility with pre-HTML4 browsers. An HTML tag is a way of describing the structure of your document. The set of elements is defined in the DTD, as are the legal attributes for each element. This means that HTML is not extensible by users, a limitation that is being changed in newer versions. Everything between is contained within the tag and referred to as the contents.
Most elements are non-empty, which is to say that they have contents and an end tag.
In HTML 4.0, the end tag always has the form shown above. The start tag may not have any attributes if the element has no attributes defined for it or if all the attributes are optional. It has optional attributes to specify the language and text direction for the document, but the default values for those will suffice for our purposes. Next is a HEAD element, containing information about the document. Following the HEAD section is the BODY tag.