A topic at WebmasterWorld raises the question on whether or not search engines (particularly Google with 71.97% of search engine market share) will index a page properly that does not contain <html></html>, <head></head>, and/or <body></body> elements. These three (03) HTML elements are optional based on the W3 Specifications.
Admin Note: The original poster at WebmasterWorld asked a question specifically about the missing <body></body> element. I've included the <html></html> and <head></head> elements as they fall under the same premise, they are optional and not required.
This page's structure is minus the optional <html></html>, <head></head>, and <body></body> elements and consists of the following simplified HTML...
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<title>Missing HTML, HEAD, and BODY Elements - Will the Search Engines Index this Page Properly?</title>
<style type="text/css">@import url("/css/seo.css");</style>
This page has been tested in multiple browsers and displays identically as if it contained the <html></html>, <head></head>, and <body></body> elements. All three of these elements have optional start and end tags.
What is the resulting effect of excluding these structural elements that we've become so accustomed to using? I know one of them...
"This page does not pass W3 Validation and has 10 Errors and 3 Warnings."