iframe source file format

in the books by aaa.html source file that is requested is a complete html file, I removed a number of

change on the inside aaa.html only

, and so on, ie, in the normal show,
is not Will be able to say that omitted the point of these labels? If it is not what will happen?
Iframe, the source document must be at least what label?

iframe's src point to a html page, usually with the same html.do not contain a complete structure of the standard html tags, because of the browser compatibility is very good, will not affect the results of any show.However
from standardization, the structure of the following is the full HTML content, or proposed to develop good habits production: