HTTP Headers

HTTP headers are sent to the client (browser) in the response from the web server before the document itself. The HTTP headers which control how an HTML document is displayed might look like this:

Content-Type: application/xhtml+xml; charset=UTF-8
Cache-Control: max-age=120
X-UA-Compatible: IE=9

When a program or server-side scripting is generating HTML, the language probably has an API to send the proper HTTP headers.

How To Set HTTP Headers
Content-Type Header for HTML
How to set the Content-Type header and other HTTP headers for HTML 5 and later versions of HTML
.htaccess Regular Expressions
HTTP URL Redirect
URL redirection or URL forwarding allows a request for one URL to be redirected to a different one, frequently used when a web page has moved, for example.