Is it necessary to write HEAD, BODY and HTML tags?

Question

Is it necessary to write , and tags?

For example, I can make such a page:

Answer 1

Omitting the html, head, and body tags is certainly allowed by the HTML specs. The underlying reason is that browsers have always sought to be consistent with existing web pages, and the very early versions of HTML didn't define those elements. When HTML 2.0 first did, it was done in a way that the tags would be inferred when missing.

I often find it convenient to omit the tags when prototyping and especially when writing test cases as it helps keep the mark-up focused on the test in question. The inference process should create the elements in exactly the manner that you see in Firebug, and browsers are pretty consistent in doing that.

But...

IE has at least one known bug in this area. Even IE9 exhibits this. Suppose the markup is this:

You should (and do in other browsers) get a DOM that looks like this:

HTML
    HEAD
        TITLE
    BODY
        FORM action="#"
            INPUT name="var1"

But in IE you get this:

HTML
    HEAD
       TITLE
       FORM action="#"
           BODY
               INPUT name="var1"
    BODY

See it for yourself.

This bug seems limited to the form start tag preceding any text content and any body start tag.