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
X-UA-Compatible: IE=9

For static web pages, the headers are provided by the HTTP web server.

• Set Content-Type using .htaccess

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

• Set Content-Type in ASP .NET
• Set Content-Type in Java
• Set Content-Type in JSP
• Set Content-Type in Perl CGI
• Set Content-Type in PHP
• Set Content-Type in Ruby on Rails