The <!DOCTYPE> declaration must be the very first thing in your HTML document, before the <html> tag. The <!DOCTYPE> declaration is not an HTML tag; it is an instruction to the web browser about what version of HTML the page is written in, gives it the information it needs to know how to render the content, what rules to follow. http://www.w3schools.com/tags/tag_doctype.asp
Metadata: information about the contents of your page. This is sometimes used by search engines to index your site. Metadata can be the doctype, html, head, content type, title, “favicon,” script and style (code or links to external pages), or other page metadata, but it is not page content.
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en“ id=“jillsalahub-writingonlineatcsu-net”> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <!--most important metadata--> <meta name=“author" content="Jill Salahub" /> <meta name="description" content="Sample XHTML and CSS Site" /> <meta name="keywords" content="CO302, Sample Site, Small Web Project, XHTML and CSS" />
Validator: a service for checking XHTML and CSS files against the rules for their use. These function as a good trouble shooting tool when checking your code, and serve as “proof” on your site of the correctness of your code. Your page has to be live on the web to validate it.
You can add validators directly to your page by including these links: <a href="http://validator.w3.org/check?uri=referer" title="Validate this page's XHTML">XHTML</a> <a href="http://jigsaw.w3.org/css-validator/check/referer" title="Validate this page's CSS">CSS</a>